add a verification step in the data retrieval process to avoid spamming
the ESO servers with invalid queries
eso: simpler return statement as per Derdon's suggestion
eso: fix function name
eso: change 'data_retrieval' to 'retrieve_data'
eso: docs data_retrieval -> retrieve datasets
eso: deprecation warning for data_retrieval
fix retrieve_data namet
ESO: warnings should only happen if there's actually a failure...
SIMBAD: mask instead of crash for VOTABLE parsing
Merge pull request #363 from keflavich/simbad_mask_bad_columns

SIMBAD: mask instead of crash for VOTABLE parsing
Merge pull request #362 from keflavich/eso_warningfix

ESO: Warning only if there really is no response
Merge pull request #357 from keflavich/eso_verbage

ESO: data_retrieval -> retrieve_data
Merge pull request #355 from keflavich/eso_verify

Add a verification step to the ESO data retrieval process