Add (picrin optional).

The library provides some macros to handle optional arguments. The
macros are compatible with those in Chicken, Gauche, etc.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
make repl tty sensitive
cosmetic change
Merge pull request #222 from omasanori/optional

Add (picrin optional).
Merge pull request #226 from KeenS/repl-batch

Repl batch
WIP: Add (picrin socket) and (srfi 106).

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