Squashed 'source/_templates/rtd/' content from commit 5324cc3

git-subtree-dir: source/_templates/rtd
git-subtree-split: 5324cc3ac343d22a64e2e4ede059fb4fef51a68b
Merge commit 'c9b5ccebb3449303e6ad81b340475e4662b310bb' as 'source/_templates/rtd'
Add the RTD theme.
Remove rtd from _templates.