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
Include string.h and stdlib.h at all time.

Even if readline support is disabled, some functions declared in
string.h and stdlib.h are used. (e.g. strlen and exit)

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