Create button plugin

Add ButtonPlugin class
Add ButtonPluginTest class
Merge branch 'master' into create-button-plugin
[WIP] ThemeInterface
Add ThemeRepositoryTest for the first time.

This test is unsolved test

1. call getAll method.
2. call get method.
Add ThemeRepositoryInterface
Add get method
Start create BrPlugin commit
Fix Markdown Extra

after `composer dump-autoload` app cannot resolv `_MarkdownExtra_TmpImpl`
Add ThemeRepositoryTest for the first time.

This test is unsolved test

1. call getAll method.
2. call get method.
Add ThemeRepositoryInterface
Add get method
Add exists method

Add getClassName method for get theme class name
Add theme exists test
Create BrPlugin.php with inline() & convert()
Create BrPluginTest.php

This is tiny test, all test green!
Modyfy test case

Fix error message in get method when there is no theme
Modify get method test with adding exception test
Add Interfaces and tests
Add Interfaces and tests
Add Theme class
Resolve conflict
Merge pull request #55 from toiee/feature-br-plugin

Create br plugin