Version bump to 0.4.0.
Also export RUBY_PATCHLEVEL (issue #62).
updated formatting and env descriptions

* Pulled in @HavenWood's chruby man page.
Renamed chruby.md to chruby.1.md.
Moved docs/chruby.1 into share/man/man1/
Added a basic man page task.
added -v, --version to OPTIONS
Use the last lexical matched ruby in RUBIES.

* This allows chruby to select the highest (lexically sorted) version.