Add tests for Sass
Fix error pattern for Sass checker
Fix usage of prompt argument
Improve the prompt in flycheck-describe-checker
Remove JSL checker

JSL does not provide proper distribution packages, making testing hard,
and seems to lack active maintenance.
Fix typos (jslint -> jshint)
Merge branch 'master' into unit-tests

* master:
  Fix typos (jslint -> jshint)
  Remove JSL checker
  Improve the prompt in flycheck-describe-checker
  Fix usage of prompt argument
  Fix error pattern for Sass checker
Add status image