Allow mapping ruby object attributes to document attributes.

[vStone]

I'm trying to use couch_potato for an existing schema (where I have no say in the contents).
It contains some interesting keys such as 'with-a-dash' or 'why_no_question?'

This obviously fails when mapping this on ruby attributes.
Perhaps it could be useful to allow:
field :my_field, couchdb_key: 'my-field'

ChatGPT helped me (poorly) to make some adjustments and get this to work. I have not tested this extensively.

If you want, I can PR my changes but you will probably have a better view on where to make these adjustments to support this.