Add support for various join types.

Fixes issue #9
Merge branch 'issue-9'
Implement tryOneRow and tryScalar.

Fixes issue #3
Refactor database._selectOneRow
Tweak _selectOneRow error messages
Add supporting test specs for tryOneRow and tryScalar
Merge branch 'issue-3'
Merge pull request #13 from dealerlogix/master

New goodies