incorporating sounds, merging andrews push to frontend
Merge branch 'frontend' of https://github.com/peterxu422/PLTCompiler into frontend
pretty print sound lits
added and tested expressions for ast
added negative operator
added prettyprint for if else statements
added test cases for front end
fixed conflicts from merging with operators in scanner and parser
added interpretation for return while and loop and (expr)
added statement test programs in lullabyte for interpreter and expected output
Created a proper makefile
made Makefile more formal
added make.sh
merged master to backend
fixed comment bug