Fix default value of helm-rb-get-methods-path

Set default path of helm-rb-get-methods-path in the same directory as
helm-rb.el.
Rename from helm-rb-get-methods-path to helm-rb-get-methods-program

According to Elisp variable name conventions. for more information, See
http://www.gnu.org/software/emacs/manual/html_node/elisp/Tips-for-Defining.html#Tips-for-Defining
Merge pull request #1 from yasuyk/patch-1

Minor improvements about helm-rb-get-methods-path