Overhauled (and moved) libsite; streamlined installation

Now that there is a libsh, it makes sense to move libsite there.

Took this opportunity to clean up the long list of messy global
environment variables therein, and thus did the same for each use-case
of these variables.

Also fixed up the makefile to ensure first-time user experience is
seamless - thanks to travis-ci this was easy to do!

Added `SITE_CORE_BIN'.

Clean-up installation/uninstallation/purge (makefiles).
New `.travis.yml': enter Travic-CI
Updated `README.md': travis and website links