0.0.0-alpha.3: Prepare for release.

- build: FIX version-check in setup.
-- Group all requirement-files into a new folder.
-- ,tests,ci: Pin pandas>=0.15.1 and re-calibrate veh-db tests.
- docs,metrics: Finalize changes in arrow-diagrams.
- rtd: TRY forcing pandas-version to fix plot-directive.