represetnations
Low-level API work
Various improvements to low-level classes
Through high-levels
More work on coordinates api
Add item illustrating non-kwarg LL class construction
high-level stuff done
c->coords
small tweak to coordinates_api_2
Clean up comments to not be "inline", as requested by @astrofrog
Implemented a variety of changes based on comments by @taldcroft, @mdboom, and @Cadair
Various typo fix and tweaks pointed out by @astrofrog
Eliminated option that had a lot of "no" votes
Added store_as back in but with a non-string example

previously it was part of the "option" block, but has uses outside that
Choose option for phi/theta based on other subclasses
`data` voted to be immutible, at least initially
framespecattrs -> frame_attr_names
Added realize_frame as suggested by @Cadair, as well as a bit more about `data`
remove OPTION around "allow raw array inputs and `units` keyword"

voted for by @taldcroft and no votes against
fix for a number of spelling typos mentioned by @astrofrog and spell check