Feature Request: add formatting toolbar

[lord-aerion]

It would be great to have a formatting toolbar. Markdown is powerful and easy to use, but it can be hard to memorize all the syntax options, especially the ones you don't use very often, or if you're a newcomer to Markdown.

Markor is a great example of this, with a scrolling toolbar at the bottom of the screen. This works even better on landscape devices (see #18) such as the Planet Computers range of devices.

[shompoe]

I don't mean to suggest that Markor is not a great example for this. But another example which works particularly well on mobile devices with limited screen space might be Outline. Formatting controls appear only when you need them to and take up no screen space at all when you don't.