Auto add parentheses

In this version, `value` and `identifier` check that:

1. If the input is a `raw`, do nothing;
2. If the input is a `_query`, add parentheses around it (turning it
into a
`raw` in the process);
3. If the input is a naive string, process it normally.

Not sure if other things will break though.
Merge branch 'auto_paren' of git://github.com/uranusjr/mosql into uranusjr-auto_paren

Conflicts:
	mosql/util.py
Merge branch 'dev' of github.com:moskytw/mosql into dev