Merge pull request #20 from gsalgado/vp

Move ExistsSeries to internal_test.go
Added empower function and test
Merge pull request #19 from jimmysong/vp

Added empower function and test
Added proper error handling to db.go, misc. spelling fixes.
Merge pull request #21 from teknico/vp

Added proper error handling to db.go, misc. spelling fixes.
Use GetSeries where possible and some cosmetic changes