Allow users to query a list of coordinates

Due to restrictions by the SDSS server it can be useful to query a list
of coordinates in a single query. The result can then be matched with
the original list by using:

dr = coords.Angle(radius).to('degree').value
obj_coords = coords.SkyCoord(result['ra'], result['dec'], frame='icrs',
unit='deg')
matches, d2d, d3d = obj_coords.match_to_catalog_sky(pos)
result = result.group_by(matches)

where the group keys are the indices to the coordinates sent to the
query.

A future modification of astroquery can do the above procedure
automatically.
corrected missing brackets, units, and parenthesis
Changed SkyCoord to commons.CoordClasses
Changed check for scalar
Merge pull request #376 from fred3m/SDSS-batch-query

Allow users to query a list of coordinates for SDSS query
irsa_dust.rst clarifications and addition of a link
ESO header schemae didn't allow lists-of-strings because of an incorrect
call
Merge pull request #379 from keflavich/eso-header-schema

ESO header schema: minor fix
State dependency versions more clearly
Merge pull request #321 from cdeil/issue_321

Unicode encoding error on Python 3.2
renamed method BaseQuery.request to BaseQuery._request
Merge pull request #380 from derdon/issue350

renamed method BaseQuery.request to BaseQuery._request
Added Miriade.query_rise_transit_set()
Move observatory codes generation to private method
request() -> _request()
Added license information
Implements ConfigItem for observatory codes and rts URL
End of file carriage return
Use ConfigItem