Major refactor of the docs, phase 1

Move to use the astropy affiliated package template for the docs,
started on a proper api doc using astropy and fixed some docstrings
add back in other doc pages
one warning in guide and other tweaks
re-add examples
add auto templates
more database guide
Merge pull request #695 from Cadair/doc_sprint

Prep for the Documentation Sprint
refactor guide
add new dirs
Merge pull request #698 from Cadair/doc_sprint

refactor guide
DocSprint: citation up to date - resolves #693
DocSprint: citation - lines break added for easier track
Merge pull request #699 from dpshelio/doc_reference

DocSprint: citation up to date
fix intersphinx
remove mock
Merge remote-tracking branch 'upstream/documentation_sprint' into doc_sprint
update doc requirements.txt
remove database guide (temp)
more database murder
remove reference to database