Added "*.o" to .gitignore.
Created Makefile for atn (NOTE: not yet linking, just compiling and fixing
errors).
Added every source file that compiles without changes (or with
minimal changes) to the Makefile default target.  Still no linking.
Merge branch 'feature/FirstPass_atn' of https://github.com/scottidler/antlr4cpp into feature/FirstPass

Conflicts:
	.gitignore

Merge the Linux work