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.

Applying the same style fixes as in #19: Running goimports (https://github.com/bradfitz/goimports) and Fatal(err) instead of Fatalf(err.Error())

Small Formatting Fixes

Fix nil panic in postgresql/result.go