Teach gyp generated Makefile to build crash_generation_app correctly

- Use linker flag for Windows subsystem
- Add rule for compiling windows resources
- rename crash_generation_app.rc to avoid a clash in corresponding .o names
Ensure the C:\Dumps\ directory exists in the crash_generation_app demo

Ensure the C:\Dumps\ directory exists in the crash_generation_app demo,
otherwise it doesn't demonstrate much.

http://code.google.com/p/google-breakpad/issues/detail?id=298
Add a README.md with notes on what is left to do