check that a source file exists before scanning it for includes
move wram constants into constants.asm; make all labels use :s

any global constants will have to be separate from any one object

there might be a better way to fix this, like pulling constants in preprocessor.py
bump extras to use globals.asm
consolidate labels across objects into globals.asm

this is required for objects to share labels
fix a typo in Makefile

we want to link more than one object!
include globals.asm in pokecrystal.asm
add globals.asm to .gitignore
Merge pull request #203 from yenatch/globals

consolidate labels across objects into globals.asm