Add StdIO library

These libraries provide an implementation of CrashCatcher which know
how to use stdin and stdout to create a hex based crash dump.  A
developer just needs to link in this library and provide a thunk for
CrashCatcher_GetMemoryRegions() to enable automatic crash dump
generation for Hard Faults.
A few minor CrashCatcher updates

* Add *.hex to .gitignore
* Update CrashCatcher.h to work from C++ source code as well.
* Add macros at bottom of CrashCatcher.h which will generate hard
  faults:
   CRASH_CATCHER_READ_FAULT
   CRASH_CATCHER_WRITE_FAULT
   CRASH_CATCHER_INVALID_INSTRUCTION
* Modified makefile to build host based unit tests before ARM libraries
  as there is no sense in building ARM libs if the unit tests are
  failing.
Adding mbed1768 test application

Adding CrashingApp as a sample application that links in the
CrashCatcher module.  It lets the user pick one of the following
scenarios before issuing a bad read to cause a crash:
* Using MSP that is 8-byte aligned at time of crash.
* Using MSP that is NOT 8-byte aligned at time of crash.
* Using PSP that is 8-byte aligned at time of crash.

I currently just have it building and running on the mbed1768 device.
I will add the mbed11u24 device in the future.

NOTE: The makefile for this sample expects GCC4MBED to be installed
      in a directory which is a sibling of this CrashCatcher
      repository.
Switch GPL license to Apache in one file

I had copied over a GPL license in one of the assembly language source
files.  I removed that license text and replaced it with the same
Apache license used everywhere else in the project.