[bugfix] propagate errors through the VM
Merge pull request #72 from koba-e964/master

[bugfix] circular-list?, proper-list?
no unistd.h in lex.yy.c
s/NORETURN/noreturn/g
publish UNREACHABLE macro
move utility macros to picrin/util.h
reafactor noreturn macro
refactor GENSYM macro
remove redundant prefixes
Merge branch 'master' of github.com:wasabiz/picrin
move global variable accessor/mutator definitions to vm.c
move irep dump function definitions to irep.h
pic_state is not used in pic_dump_*
POPN macro was not used
refactor analyzer
refactor analyze_var
refactor analyze_args
remove redundant arena management
cleanup
add xvect