add src/sink fields to pic_port object
add functions which will proceed I/O with picrin objects
add call-with-input-file and call-with-output-file
Use C99 + GNU extensions (-std=gnu99) by default.

Without -std=* option, gcc assumes it is gnu89 source, though clang does
it is gnu99 source.

I'd suggest using gnu99 by default. We are in the 21st century.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>