Save time zones in postgres driver

The current format doesn't save the time stamp, which leads to undefined behavior when updating a TIMESTAMP WITH TIME ZONE column.

SQLite: Fixing sqlutil functions. Scope revision (Table, Source, Tx, Result should not be exported), mild golint review (unused/uncommented globals).

Documentation: Updating README.md to reflect status on database transactions and main.go to reflect newly introduced features.

PostgreSQL: don't set 'user' or 'pass' in conn string when not provided

Causes the driver to fail silently if none is provided.