move rSYMBOLs from pic_state to codegen_state
add sSYMBOLs to pic_state
add analyzer prototype
arena management
fix some bugs
typo
change lookup_var API
initialize with global scope
remove unused properties
add pic_list_ref
add pic_compile
cleanup
unify the names of IR reference nodes to a name 'ref'
add depth property
Merge branch 'master' into analyzer

Conflicts:
	include/picrin/pair.h
	src/pair.c
start using pic_list_ref and pic_list_tail
rename include guards
add cv_foo properties to codegen_context
change analyze_args API
change ast format