Changes themes displaying RVM or other Ruby version info to use the central
ruby_prompt_info function. This supports more Ruby versioning mechanisms,
reduces copy-and-paste code, and avoids "zsh: no such file or directory: rvm-prompt"
when run on machines that do not have RVM installed.
Changes the prefix/suffix variable names to ZSH_THEME_RUBY_PROMPT_PREFIX and
ZSH_THEME_RUBY_PROMPT_SUFFIX, since they apply to all Ruby versioning mechanisms,
not just RVM.
Allows empty ZSH_THEME_RUBY_PROMPT_PREFIX and ZSH_THEME_RUBY_PROMPT_SUFFIX.
Initializes jenv and provides the jenv_prompt_info funtion to add
Java version information to prompts. This function is stubbed in
prompt_info_functions script to allow it to be safely called
regardless of whether or not the jenv plugin is loaded.
It also splits detection of the plugin/versions directory and bin directory
to suppport the way Homebrew splits the jenv bin and data directories