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

* proc: Refactor stackIterator to use memoryReadWriter and BinaryInfo

* proc: refactor EvalScope to use memoryReadWriter and BinaryInfo

* proc: refactor Disassemble to use memoryReadWriter and BinaryInfo

* proc: refactor BinaryInfo part of proc.Process to own type

The data structures and associated code used by proc.Process
to implement target.BinaryInfo will also be useful to support a
backend for examining core dumps, split this part of proc.Process
to a different type.

* proc: compile support for all executable formats unconditionally

So far we only compiled in support for loading the executable format
supported by the host operating system.
Once support for core files is introduced it is however useful to
support loading in all executable formats, there is no reason why it
shouldn't be possible to examine a linux coredump on windows, or
viceversa.

* proc: bugfix: do not resume threads on detach if killing

* Replace BinaryInfo interface with BinInfo() method returning proc.BinaryInfo