New Formula: linenoise

A small permissively licensed alternative to readline and libedit.

Currently HEAD only.
New Formula: mruby

Mostly a copy of the mruby formula in Homebrew core, but with some subtractions
and custom patches:

  - Don't install mrubygems or mrubylib folders.

  - Build with Clang by default.

  - Enable linenoise support in mirb.