Add ability to use coord instance in SHA

I updated the `astroquery.sha` module to parse an `astropy.coordinates` instance. This update should be independent of upstream updates in astropy as long as the coordinate transformation methods stay the same:
```python
ra = foo.fk5.ra.degrees
dec = foo.fk5.dec.degrees
```
where `foo` is a coordinate instance.

I also updated the doc-string, docs-page, and fixed a bug in the `lamda` and `sha` modules to import all of the relevant functions (`__all__` was missing a few items).