Update Documentation for 5.2.0

[aaronayres35]

targeting [gh-pages]

This PR follows the lead of #770

These are the steps I followed for building the documentation:

git clean -ffxd
git checkout 5.2.0
python ci/edmtool.py install
edm shell -e enable-test-3.6-null
python setup.py install
exit
python ci/edmtool.py docs
# move docs/build/html folder to my desktop
git checkout gh-pages
git clean -ffxd
git pull
git checkout -b gh-pages-5.2
mkdir 5.2
# move html folder containing built docs into cwd
rsync -r --exclude="\.buildinfo" html/* 5.2/  # put 5.2 built docs in 5.2 folder
rm -r `ls -d [![:digit:]]*`  # remove 5.1 docs from root dir (they are still in 5.1 folder)
cp -r 5.2/* .
git add .
git commit -m "replace 5.1 built docs with 5.2 built docs, also store 5.2 docs in 5.2 folder"

To test:
python -m http.server

[rahulporuri]

LGTM. I served the docs locally and browsed through the 5.2 docs and tested that the older (5.1) docs are still available under 5.1/*