Documentation updates

[tonio-ramirez]

The documentation seems a bit incomplete. Looking through issues and commits, I see references to "bootstrap" mode and/or "bootstrap.properties", but don't see it mentioned anywhere in the documentation. Ditto for specifying both an appdir and an appbase. As far as I can tell, appdir is the argument to java -jar getdown.jar, required, and appbase is a required entry in getdown.txt, so I don't quite understand references like "If you run Getdown with an appbase and an appdir", as in 469f4fe.

Additionally, it would be nice to see which features were introduced in which versions. I'm currently working on a project that, at least for now, requires Java 6, so I'm forced to use version 1.6.4 (the latest version that supports Java 6, from what I can tell), and have run into features that don't seem to be supported (e.g. ui.min_show_seconds).