Instead of unconditionally returning all present goroutines,
GoroutinesInfo now allows specifying a range (start and count). In
addition to the array of goroutines and the error, it now also returns
the next goroutine to be processed, to be used as 'start' argument on
the next call, or 0 if all present goroutines have already been
processed.

This way clients can avoid eating large amounts of RAM while debugging
core dumps and processes with a exceptionally high amount of goroutines.

Fixes #1403

This patch allows the `trace` CLI subcommand to display return values of
a function. Additionally, it will also display information on where the
function exited, which could also be helpful in determining the path
taken during function execution.

Fixes #388

Add a flag to Stackframe that indicates where the stack frame is the
bottom-most frame of the stack. This allows clients to know whether the
stack trace terminated normally or if it was truncated because the
maximum depth was reached.
Add a truncation message to the 'stack' command.

Adds -defer flag to the stack command that decorates the stack traces
by associating each stack frame with its deferred calls.

Reworks proc.next to use this feature instead of using proc.DeferPC,
laying the groundwork to implement #1240.

This pull request makes several changes to delve to allow headless
instancess that are started with the --accept-multiclient flag to
keep running even if there is no connected client. Specifically:

1. Makes a headless instance started with --accept-multiclient quit
    after one of the clients sends a Detach request (previously they
    would never ever quit, which was a bug).
2. Changes proc/gdbserial and proc/native so that they mark the
    Process as exited after they detach, even if they did not kill the
    process during detach. This prevents bugs such as #1231 where we
    attempt to manipulate a target process after we detached from it.
3. On non --accept-multiclient instances do not kill the target
    process unless we started it or the client specifically requests
    it (previously if the client did not Detach before closing the
    connection we would kill the target process unconditionally)
4. Add a -c option to the quit command that detaches from the
    headless server after restarting the target.
5. Change terminal so that, when attached to --accept-multiclient,
    pressing ^C will prompt the user to either disconnect from the
    server or pause the target process. Also extend the exit prompt to
    ask if the user wants to keep the headless server running.

Implements #245, #952, #1159, #1231

* command/terminal: allow restart to change process args

Add -args flag to "restart" command. For example, "restart -args a b c" will
pass args a b c to the new process.

Add "-c" flag to pass the checkpoint name. This is needed to disambiguate the
checkpoint name and arglist.

Reverted unnecessary changes.

* Applied reviewer comments.

Vendored argv.

Change the syntax of restart. When the target is is in recording mode, it always
interprets the args as a checkpoint. Otherwise, it interprets the args as
commandline args. The flag "-args" is still there, to handle the case in which
the user wants to pass an empty args on restart.

* Add restartargs.go.

Change "restart -args" to "restart -noargs" to clarify that this flag is used to
start a process with an empty arg.

* 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

Implements #727

* service/debugger: Restore breakpoints using file:line on restart

Restoring by address can cause the breakpoint to be inserted in the
middle of an instruction if the executable file has changed.

* terminal: Warn of stale executable when printing source

Adds ability to load x87, SSE and AVX registers.

Fixes #666

This version preserves the order of requests, allows the
client to switch between API versions and introduces a
way to send notifications to the client (see TODO item at:
proc/proc_linux.go:325).

Fixes #523, #571

* proc: bugfix: StepInto can not function when temp bps exist

* terminal,service: auto-continue during next and step

Make dlv call continue automatically when a breakpoint is hit on a
different goroutine during a next or step operation.
Added API hooks to implement the other solution to this problem (cancel
the next/step operation if a different breakpoint is hit).

Fixes #387

* documentation: headless invocation should specify --api-version=2

* documentation: More API documentation

* documentation: copied documentation from client.go to rpc2/server.go

Fixes #164

* service/api: Removed unused fields of service/api.Function

* proc/eval: Set return variable name to input expression

* all: fine-grained control of loadValue for better variable printing

Makes proc.(*Variable).loadValue loading parameters configurable
through one extra argument of type LoadConfig.
This interface is also exposed through the API so clients can control
how much of a variable delve should read.

New API version with better backwards compatibility plus mechanism to
select the API version that a headless instance should use.

Adds service/test/cmd/typecheckrpc.go to type check the RPC interface.