Fixes a code path where stacktrace returns < 2 locations and
thread.ReturnAddress would panic. Now returns an error.

Major source cleanup, still not finished. Removes gross control flow.

* Cleanup comments
* Cleanup naming in certain instances
* Modify stacktrace to return current location

Finishes #63 #64

Process is an incorrect name for the DebuggedProcess struct that the
thread is "a part" of. Also, no need to export that field.

* Properly find next source line for goroutines blocked in chanrecv
* Refactor breakpoint clearing
* Refactor temp breakpoint setting