Changed angle unit methods to reflect new names (singular, not plural)

Closes #112
Use new astropy names for coordinate objects

Closes #123
Check explicitly for warnings about missing object list
Use astropy coordinate arrays instead of array of coordinates.
Whitespace clean up
Delete debugging lines that were commented out
Test whether object adder detects an ambiguous list of objects
Raise error if list of objects is ambiguous
Add documentation of function argument
Add check that length of input arrays are consistent

As a bonus, this includes a hack for finding the length of an array of coordinates in astropy.
Correctly handle check for duplicate objects in catalog in case when there is only one object
Initial implementation of object matching using astropy-0.3 coordinates
Remove test that no longer makes sense after object matching refactor
Change order of tests to be easier to follow
Remove as many instances of hard-coded test file name as possible
Add test image that does not match any objects in test catalog
Remove find_object_match because functionality is now built into astropy
Copy everything in test/data instead of only one file
Fix bug exposed by previous commit
Handle NameResolveError in coordinate lookup from object name

Closes #124