Release 1.5.6-beta.0

• WIP (d8faa70)
• WIP (998bf19)
• WIP (8a703b7)
• WIP (7fed779)
• Update installation instructions (29d13ef)
• Move the react-on-rails-pro renderer to subdirectory (d55d066)
• Update and simplify Gemfiles (#142) (7aa5712)
• Update loadable example (#141) (4c3f402)
• Fix invalid error message (#138) (078a149)
• Update CHANGELOG.md (bed03c1)