Ignore backup files

GitHub: fixes #21

Reported by TOMITA Masahiro. Thanks!!!
Require Ruby 1.9.3 or later
Fix wrong exception class name...

Reported by Junichi Oya. Thanks!!!
Add workaround for Ruby/GLib2 2.0.2 or earlier
Add 2.1.0 entry
2.1.0 has been released!!!
Bump version

2.1.0 ->
2.1.1
    ^
Fix wrong require file

GitHub: fix #25

Reported by Yoshihide Chubachi. Thanks!!!
Add 2.1.1 entry
Rabbit 2.1.1 has been released!!!
Bump version

2.1.1 ->
2.1.2
Fix a typo

It fixes an error for rabbit-slide without arguments:

    % rabbit-slide
    lib/rabbit/command/rabbit-slide.rb:232:in `default_command': undefined method `file' for File:Class (NoMethodError)
            from lib/rabbit/command/rabbit-slide.rb:65:in `parse_command_line_arguments'
            from lib/rabbit/command/rabbit-slide.rb:46:in `run'
            from lib/rabbit/command/rabbit-slide.rb:33:in `run'
            from bin/rabbit-slide:22:in `<main>'
info-window: support auto source reload

GitHub: fix #23

Reported by Kazuhiro NISHIYAMA. Thanks!!!
Add link pixman procedure before install pango

cf. "Error: You must `brew link pixman' before pango can be installed"
doc en: apply Homebrew install documentation improvemnt in Japanese

Pixman should also be linked.
doc ja: update the Ruby Installer version
doc en: update the Ruby Installer version
doc: rabbiter 2.0.1 has been released!!!
Use gettext 3.0.0 or later
Use https for RubyGems.org