The `share/ruby-build/` directory from each rbenv plugin, if it exists,
is added to RUBY_BUILD_DEFINITIONS automatically during `rbenv install`.

Support extra definitions paths via RUBY_BUILD_DEFINITIONS

Closes #609

This is a colon-separated list of directories that will get searched for
build definition in order from left to right.

This is to allow specifying an alternate path where `share/ruby-build/*`
definitions reside. Useful in tests as well.

Add link to suggested build environment to README

Add rbx-2.2.10

add jruby-1.7.13

Add rbx-2.2.9, 2.2.8 was skipped due to broken wrappers.

Fix `fetch_git` with `--keep`

Update existing git repo if exists, or clone if not exists.
The destination repo might exist if the `--keep` was supplied for `ruby-build`.

OpenSSL library updated to 1.0.1h

Previous versions of the library contain a vulnerability CVE-2014-0224.

The script handles bumping up the version number, committing, tagging
and updating the Homebrew formula. The last step requires `hub` to be
installed in order to submit a pull request to Homebrew.

/cc @sferik @hsbt

[ci skip]

Fixes #548, closes #551

This is so any 3rd-party definitions continue to work even if they have
MD5 checksums embedded.

A more secure hashing algorithm makes it less feasible to serve up a
modified tarball that matches the same checksum.

See the discussion in #548

add rbx-2.2.7

added definition of 1.9.3-p547

This reverts commit d45f1451, reversing
changes made to 13de5110.

Added definition of 2.0.0-p481

Ruby 2.1.2 is released!