Tidy data

[SaturnFromTitan]

Currently reports are returned in the standard format received from the API. Some basic cleaning would be helpful. I'm thinking of...

• convert micro conversions to actual currency (e.g. budget, AvgCpc, Cost, ...)
• convert " --" to np.nan (Criteria in KeywordsReport for Display accounts)
• convert auto:xyz to xyz and create a separate column for the bidding type (MaxCpc)
• ...

There's already a helper module for micro conversions, so that'd be a good starting point.