Add asciidoc build back in the Documentation folder

Although we now build the documentation with buck, the asciidoc
build is much faster and more convenient for quickly generating
html files while making documentation updates.

Note that due to some asciidoctor specific formatting, not all of
the documents render correctly with asciidoc.

This should of course not be used for verifying documentation
changes, or for building any official documentation.

Change-Id: I92ecde69e066d08920a1b419e76bf594e87c9bd3
3 files changed