added command line interface support based on symfony/console #2
added a note.

hope it will help someone.
updated readme

* added CLI section
* added a notice line
added "bin" section to composer.json
added `compile` command #2
added tests for gfm tables #2

still needs more tests
added getAttributes method
added gfm table support #2

To activate it:
    $ciconia->addExtension(new \Ciconia\Extension\Gfm\TableExtension());