Squashed 'doc/' content from commit 98a8255

git-subtree-dir: doc
git-subtree-split: 98a82552d3eac33272de151ac2d1ac6b7c8144d4
Merge commit '7d07d8579de05ed485d247210c91a3dea5e226db' as 'doc'
Revert "Merge commit '7d07d8579de05ed485d247210c91a3dea5e226db' as 'doc'"

This reverts commit 33e2cca409dd5cc3b549e04f3f4b64a39854be0b, reversing
changes made to 7e2d9c4a96bb11741a94649b6d55809d0a406b86.
added html documentation
Added reference to ET online manual from the title page