Add user parameter to rbenv class
Add user parameter to rbenv::install resource
Add user parameter to rbenv::plugin resource
Default rbenv_root to /usr/local/share/rbenv
Change rbenv::build install exec to depend on rbenv class too

Should ensure that the default-gems and other plugins get installed
properly before any rubies are built.
Re-order rbenv bin and shims in PATH
Add rbenv::config resource
Whitespace cleanup in rbenv::install
Update rbenv::ruby resource.

Create an rbenv directory in the users homedir and and symlink their
versions/$version to shared versions directory.