Add MIT/GNU Scheme (v9.2)

Uses MIT/GNU Scheme x86-64 package to install a package for Scheme.
Config options and install is standard using the `prefix_path`.

Displays a tip with the URL of the online documentation after install
is complete.
Merge pull request #194 from elskwid/add-mit-gnu-scheme

Add MIT/GNU Scheme (v9.2)