Add --cleanup option.

Adds an optional --cleanup option flag to remove the downloaded archive and any unpacked source, as suggested in #116.
Added Rubinius 2.2.6.
Fix spelling in ruby-install manpage
Correct grammer in manpage
Merge pull request #133 from gevans/typo-correction

Fix spelling in ruby-install manpage
Grammar nit fix.
prune installation directories that no longer exists from `make install`
Merge pull request #139 from wilmoore/prune-unused-dirs

prune installation directories that no longer exists from `make install`
Remove 2>/dev/null silencing.
Install bundler globally if it isn't available (closes #130).

* ruby-install assumes that rbx will be configured/built using the
  system ruby, which it installs via the package manager.
* On OSX system ruby is already present. OSX users are encouraged to
  upgrade to Mavericks, which provides ruby 2.0.
* Ergo, install bundler via `sudo gem install bundler`.
Expand relative --install-dir paths (closes #134).
Quote all string variables.
Revert "Expand relative --install-dir paths (closes #134)."

* This reverts commit d6618fd541830abf45ebb0b357743e671e4fd5cf.
* Does not account for ~/foo or ~foo/bar.
Call autoreconf if configure.in is newer than configure.in (closes #58).
Updated CONTRIBUTING.
Install bundler into vendor/gems/ and directly invoke bundle (issue #130).
Quote string.
Export $PATH as well.
Version bump to 0.4.2.
Updated the ChangeLog for 0.4.2.