ruby-build 20121227
Update share/ruby-build/rbx-2.0.0-dev

Rbx 2.0.0-dev need yaml install like rbx 2.0.0-rc1
Delegate to `rbenv-help` for usage, if available
Fix `rbenv-help` invocation
Add summary lines for `rbenv install` and `rbenv uninstall`
Point people to the readme
Added a recipe for JRuby 1.7.2.
Merge pull request #262 from nirvdrum/add_jruby_1.7.2

Added a recipe for JRuby 1.7.2.
ruby-build 20130104
Definition for ruby 2.0.0-rc1
Merge pull request #265 from mariochavez/master

Add definition for Ruby 2.0.0 rc1
Add 1.9.3-p374
Merge pull request #269 from sorah/193p374

Add 1.9.3-p374
Invoke chmod for group or world writable directories only
ruby-build 20130118
Support selection of 'make' tool via environment variable
Merge pull request #272 from onibox/make-env-var

Support selection of 'make' tool via environment variable
Merge pull request #271 from nobu/master

No needs to chmod all directories.
Update examples
Allow plugins to run code before and after the installation process