Updated documentation

[Alan DeKok]

  We've updated the corporate site (http://networkradius.com), so it's a bit prettier.  As part of that re-write, we've moved the documentation to using gitbook.  It's not perfect, but it's a lot better than it was before.

  Please check out:

http://networkradius.com/doc/current/

  It has a nice table of contents, good formatting, and tons of cross-links for each page.

  We're working on adding more documentation over the next few months, too.

  Alan DeKok.