Use absolute paths for setting BUNDLE_BUILD__RGEO
update build pack tag in README
Added ability to override s3 bucket where files are downloaded from with
environment variable
change libraries installation directory

Changed install directory from vendor/<library>/<version>/ to instead
install it all in .heroku/vendor so that this plays nice with other
buildpacks, such as heroku-buildpack-python.
fix typo
make support only upload files
Use stack name as namespace
Add some documentation.
Merge branch 'master' of https://github.com/cyberdelia/heroku-geo-buildpack

Conflicts:
	bin/compile