Work-in-progress to address issue #50 (installation documentation)

An attempt to address #50. See commit description for 1e3dcac. The "HowToBuildFromSource.." documents have been moved to Markdown, but have not otherwise been updated to reflect how to properly install now.

Still to do:
- Update the documentation to reflect proper installation procedure.
- Update README.md quick-install/build documentation.

This PR is not ready to be merged in yet. Just looking for feedback. We may not even want to do any of this!

By the way, on my computer, doxygen fails to build completely. It gets hung up at `Generating docs for compound SimTK::EllipticalPointContact...`.
 
Related issue: #55.