Add LibraryLocation class
Use library response from BiblioCommons docs. Add library location response
Expect only library JSON object in constructor. In #locations, don't
flatten to a singe hash, but return an Array of LibraryLocation
objects.
Add Library tests
Add gibberish response
Let client#get check for specific fields

Some client methods took the response, picked out a particular field
from the JSON and passed that to a constructor for the object
represented by that field. We should check that that field exists
rather than constructing an empty object. Centralize this checking
in the #get method.