Try re-arranging top-level docs
Change default sphinx theme to ReadTheDocs for local build

This will make it easier to see how document changes will look on RTD without needing to push them to github
Standardize header markup and add overview
Extensively revise docstrings
Add detail to table_tree docs
Fix installation instructions for bumpy and add API for image management
Document ImageWithWCS class and add to image management page
Remove outdated documentation links
Update docstrings for everything in header_processing
Whitespace and other minor fixes
Fix installation instructions for numpy/scipy
Reorganize and extend script documentation
Extend descriptions in the overview
Reorganize index
Add templates used by astropy Sphinx extension
Use astropy Sphinx extensions in conf

Also sets a configuration item for newer versions of numpydoc that suppresses many, many, many warnings.
.gitignore the api subdirectory
Whitespace fixes
Edits for clarity
Merge branch 'new-docs'

Conflicts:
	docs/index.rst