implement load procedure
= procedure is brokwn
[bugfix] native operators such as = or + are not inline-expanded
publish pic_load
use pic_load to load built-in.scm
add missing trailing comma
[WIP] replace FILE* with my own FILE structure (pic_file *)
[WIP] add generic file object constructor (pic_funopen)
declare some low-level file IO operation methods
add string IO wrapper function prototypes
replace old stdio functions with picrin's wrapper impls
impl pic_fopen and pic_close. add FILE*-pic_file* adapter functions.
impl char/string IO functions
add IO buffering (setvbuf)
impl pic_fflush
[bugfix] call setvbuf in pic_file constructor
impl pic_fwrite with simple buffering
add missing includes
impl pic_fread with buffering
[WIP] add a buffer for ungetc