add pic_dict_new
add attribute information to closure objects
add attribute function
Merge branch 'closure-attribute'. close #124
remove get_var_from_proc (essentially the same as pic_unwrap_var)
remove var accessor and mutators
add pic_funcall
don't use pic_defvar
get rid of doubled semicolons
improve error message
refactor var. c api no longer supports converters.
add pic_set_c[ad]r
manage values in a stack
[WIP] refactor parameterize