improve downloading dependencies

no longer need to download depedencies via downloading the source.
This gets us one step closer to finishing up #31 and while making #86
 more likely to work.
use bintray in install script

no longer using github at all, or the source code.  This will make
installation far less brittle.

Issue #31
handle versioning better

an MDOC_VERSION file is created so we don't try to install the app
multiple times
Merge pull request #87 from metridoc/use-bintray-for-install-31

Use bintray for install 31