handle runtime error
add string type
add OP_PUSHCONST
read strings
take care of escaped characters in string
pic_get_args supports strings
cleanup
add system.c
return #f if get-environment-variable refers undefined env-var
add pic_list_p
add exit and emergency-exit
pic_get_args supports optional argument
exit functions take an optional argument
add aux object field to proc object
since pic_string is a first-class value, move it to value.h