Porting introduction section of Faunus manual

I've brought over most of the images as-is.  This commit is slightly
more than a pure markup conversion: it also includes a little bit of
editing to attempt to replace references to "Faunus" with
"Titan-Hadoop" or just "Titan" if the context already strongly
connotes Hadoop.  I also dropped or spliced some content that only
made sense for Faunus as an independent project (like its own
downloads page and separate javadoc URL).
Rough conversion of Faunus wiki to AsciiDoc

The terms "Faunus" and "Titan-Hadoop" are used inconsistently.
Command output and configuration file samples refer to
FaunusGraph/HadoopGraph inconsistently; same goes for other classes
renamed in the integration as titan-hadoop.

I think the syntax is mostly or entirely converted, but the content
needs substantial editing and proofreading.