Add Readline support to Ruby on Mac OS X

1. NOTE: guard-zeus causes issues when typing into the Pry session.
   1. See: https://github.com/guard/guard-zeus/issues/18 for a workaround

1. Adding Readline support to Pry

If you are on Mac OS X and have problems with either Guard not reacting to file changes or Pry behaving strangely, then you probably suffer under a Ruby build that uses `libedit` instead of `readline`.

If you are not using Mac OS X or are using JRuby, then you’re fine.

1. Option 1: Using a pure Ruby readline implementation

The easiest way to get a working readline implementation is to install [rb-readline](https://github.com/luislavena/rb-readline), a pure Ruby readline implementation. You can install it by simply adding

group :development do
  gem 'rb-readline'
end

to your `Gemfile` and install it with `bundle exec`.

1. Option 2: Build Ruby With GNU Readline Using RVM

You can use RVM to build your Ruby with GNU readline support. First, install the readline package with RVM:

$ rvm pkg install readline --verify-downloads 1

Then configure RVM to use the readline package by adding

ruby_configure_flags=--with-readline-dir="$rvm_path/usr"

to `~/.rvm/user/db`. Finally, you need to reinstall your Ruby of choice:

$ rvm reinstall 2.3.1

1. Option 3: Build Ruby With GNU Readline Using RVM and Homebrew

You can also install the latest Readline with [Homebrew](http://mxcl.github.com/homebrew/). First install Readline:

$ brew install readline
$ brew link --force readline

Then configure RVM to use the Homebrew readline by adding

ruby_configure_flags=--with-readline-dir=/usr/local/opt/readline

to `~/.rvm/user/db`. Finally, you need to reinstall your Ruby of choice:

$ rvm reinstall 1.9.3

1. Option 4: Build Ruby With GNU Readline Using rbenv, ruby_build and Homebrew

As a rbenv user, you can install readline and ruby_build with Homebrew:

$ brew install readline ruby-build

now set the configure options when compile Ruby:

$ RUBY_CONFIGURE_OPTS=--with-readline-dir=`brew --prefix readline` rbenv install 2.3.1