Add to-sql-time

I couldn't find "to-sql-time" despite java.sql.Timestamp getting imported. I'd very much like to not having this floating around in my models.clj in future, so here you go.
to and from sql-time implemented. tests for to and from added. Added mention in README.
Merge pull request #76 from bitemyapp/patch-1

Add to-sql-time
Adds MySQL time format to default parsers.
Merge pull request #79 from MichaelDrogalis/master

Adds MySQL time format to default parsers.