Support for position independent executables (PIE) on the native linux
backend, the gdbserver backend on linux and the core backend.
Also implemented in the windows native backend, but it can't be tested
because go doesn't support PIE on windows yet.

With this syntax users do not need to type the concrete type of an
interface variable to access its contents. This also sidesteps the
problem where the serialization of a type by go/printer is different
from the one used for debug_info type names.

Updates #1328

Go allows converting a single integer value to string, resulting in a
string containing a single unicode rune with the same code as the value
of the integer.
Allow the same conversion to happen.

Fixes #1322

Normally variables that have a named struct as a type will get a
typedef entry as their type, sometimes however the Go linker will
decide to use the DW_TAG_structure_type entry instead.

For consistency always wrap a struct type into a typedef when we are
creating a new variables (see comment in newVariable for exceptions).

This fixes a bug where it would be impossible to call methods on a
global variable.

Evaluates var.method expressions into a variable holding the
corresponding method with the receiver variable as a child, in
preparation for extending CallFunction so that it can call methods.

Changes (*Variable).setValue so that it can be used in CallFunction to
set up the argument frame for the function call, adding the ability to:
- nil nillable types
- set strings to the empty string
- copy from one structure to another (including strings and slices)
- convert any interface type to interface{}
- convert pointer shaped types (map, chan, pointers, and structs
  consisting of a single pointer field) to interface{}

This covers all cases where an assignment statement can be evaluated
without allocating memory or calling functions in the target process.

Implements the function call injection protocol introduced in go 1.11
by https://go-review.googlesource.com/c/go/+/109699.

This is only the basic support, see TODO comments in pkg/proc/fncall.go
for a list of missing features.

Updates #119

If the application being debugged imports two packages with the same
name (but different paths) there was no way to disambiguate the two,
since the character '/' can not appear inside a go identifier.

By allowing users to use a string literal as the package name a package
path can be specified.

Change the linux verison of proc/native and proc/gdbserial (with
debugserver) so that they let the target process use the terminal when
delve is launched in headless mode.

Windows already worked, proc/gdbserial (with rr) already worked.
I couldn't find a way to make proc/gdbserial (with lldb-server) work.

No tests are added because I can't think of a way to test for
foregroundness of a process.

Fixes #65

Change evaluation of binary operators so that both && and || only
evaluate their second argument conditionally, like go does.

Fixes #1151

The proper way to stop a running process is to call RequestManualStop,
which most code already did with the exception of some old test code.

debug_info entries can use DW_AT_abstract_origin to inherit the
attributes of another entry, supporting this attribute is necessary to
support DW_TAG_inlined_subroutine.

Go, starting with 1.10, emits DW_TAG_inlined_subroutine entries when
inlining is enabled.

Much like the bug in issue #1031 and commit
f6f6f0bf pointers can also escape to
the heap and then have a zero address (and no children) when we
autodereference.

1. Mark autodereferenced escaped variables with a 0 address as
   unreadable.
2. Add guards to the pretty printers for unsafe.Pointer and pointers.

Fixes #1075

If 'iv' is an interface variable with a struct as a concrete value let
'iv.A' evaluate to the access to field 'A' of the concrete value of
'iv'.

Replace the unsafe.Pointer type of the buf field of channels with the
appropriate array type, allow expressions accessing member field of the
channel struct.

Fixes #962

* string to []rune
* string to []byte
* []rune to string
* []byte to string
* any pointer to uintptr

The string, []rune, []byte conversion pairs aligns this to the go
language.
The pointer -> uintptr conversion pair is symmetric to the uintptr ->
pointer that we already have.

Also lets the user specify any size for byte array types instead of
just the ones already used by the program, this can be used to read
arbitrary memory.

Fixes #548, #867

Fixes #959

Fixes #940

go1.9 no longer needs "linkmode internal" on windows.

Fixes #755
Fixes #477
Fixes #631

Before go1.9 embedded struct fields had name == "" in runtime and ==
type name in DWARF. After go1.9 both runtime and DWARF use a simplified
version of the type as name.
Embedded structs are distinguished from normal fields by setting a flag
in the runtime.structfield, for runtime, and by adding a custom
attribute in DWARF.

Fixes #904

The concrete value of an interface is always stored as a pointer inside
an interface variable. So far we have followed the memory layout and
reported the type of the 'data' attribute of interfaces as a pointer,
however this makes it impossible to distinguish interfaces with
concrete value of type 'A' from interfaces of concrete value of type
'*A'.

With this changeset when we autodereference pointers when the concrete
type of an interface is not a pointer.

* Fix various issues detected by megacheck

I've ran honnef.co/go/tools/cmd/megacheck and fixed a few of the
things that came up there.

* Cleanup using Gogland

If we don't fill the Len field there will be no way for the user to
distinguish maps we didn't load from empty maps.

Buckets of maps with zero sized value types (i.e. map[T]struct{}) have
zero length value arrays.

Implements #727

Go recently introduced proposal tags to their version tags, we
are simply allowing delve to handle it appropriately.

See:
https://github.com/golang/go/commit/0954fdd51e390e209317d4652d7effc15512fd50

- moved target.Interface into proc as proc.Process
- rename proc.IThread to proc.Thread
- replaced interfaces DisassembleInfo, Continuable and
  EvalScopeConvertible with Process.
- removed superfluous Gdbserver prefix from types in the gdbserial
  backend.
- removed superfluous Core prefix from types in the core backend.

- move native backend to pkg/proc/native
- move gdbserver backend to pkg/proc/gdbserial
- move core dumps backend to pkg/proc/core

According to https://golang.org/cmd/go/#hdr-Test_packages
service_test is more appropriate becuase this directory contains
no non-test code and the intention is to compile these *_test.go
files as a separate package and link/run with the main test package.