Fix error in extracting archive versions

Version number was not being properly extracted from the archive.

Archive URL was not updated with suffix based on type.

Force archive to be installed from source

CRAN archives do not have binaries, just source.

Fixed tests

Tests were not checking extension of source from root but from archive
Archive versions have tar.gz extension
Merge pull request #21 from KentonWhite/master

Fix problems installing from Archive
Merge pull request #23 from yoni/master

Add Travis CI support.
Fix tempdir problem. Fixes #25.
Prepare for release.