Update docs and add test files

[astrofle]

Updated docs and added test files for Doppler corrections.

The documentation updates are in response to the beta testing feedback.
See Issue #148

[mpound]

For each scan in the summary() row, dysh takes the mean of numeric columns
VELOCITY, RESTFREQ, DOPFREQ, AZIMUTH, ELEVATIO
so these may differ from GBTIDL if it is reporting only the first integration values. (If verbose=True you get all the integrations)

Please update the note.

[mpound]

See conversation about other numeric columns being averaged. Docs should be tweaked.

[astrofle]

Tweaked the note to include the missing columns.