merge
Merge branch 'master' of https://github.com/boy69162000/NCTUCS_Compiler_HW1

Conflicts:
	test/sample6.ac
Merge branch 'master' of https://github.com/boy69162000/NCTUCS_Compiler_HW1
const folding.
Merge branch 'master' of https://github.com/boy69162000/NCTUCS_Compiler_HW1
const folding in parser