Add syntax checker for Handlebars using Handlebars compiler
Merge branch 'master' into yasuyk-handlebars

* master: (28 commits)
  Boldly add myself to the credits
  Remove duplicated credits
  Demote Rubocop convention messages to info level
  Update credits
  Fix test cases
  Fix error sorting stability
  Restore proper order of error tokens
  Refactor ruby test cases
  Remove ruby and ruby-jruby checkers [#250]
  Update changelog
  Install Ruby headers to build native extensions
  Fix test case names
  Add key binding to set the executable
  Warn about non-interactive use of -set-checker-executable
  Add executable variable to syntax checker docs
  Add command to select the syntax checker executable
  Add executable variables for syntax checkers [#143]
  Remove superfluous test case
  Require plain strings for checker executables
  Split Emacs command variable into executable and args
  ...
Fix Handlebars URL
Update credits and changelog
[Fix #270] Merge branch 'yasuyk-handlebars'

* yasuyk-handlebars:
  Update credits and changelog
  Fix Handlebars URL
  Add syntax checker for Handlebars using Handlebars compiler