Aper adding wcs and support for various input data

I think this one needs more work, but can be merge as is if you prefer:

- [x] support more input data types
- [x] add unit test
- [x] add/change documentation
- [x] support more input coordinate formats
- [x] return user input coordinates and pixelcoordinates in the result table

Future:
~~accept non pixel unit for radius etc. when the wcs is provided.~~ Moved to future feature list in #131

@bsipocz - actually you won't need to worry about that logic soon, see https://github.com/astropy/astropy/pull/2855 for an example of a decorator that will automatically deal with ``NDData`` objects. We can make decisions about what overrides what there.