added editor.value() method as both setter and getter

[jywarren]

Followup on using editor.value() to get/set editor content for all three modes in this issue: #15

Manually tested; i didn't see a test suite but would be happy to add a test if there is one. Thanks!

[bevacqua]

Awesome stuff. I would rather parse the user input. As long as arguments.length === 1, use String(text) to set the value to their input. In case of HTML mode, convert the provided input into HTML by way of parseHTML. Only accepts Markdown (for a simpler API).

Needs docs update

[jywarren]

OK, updated, I think; can you confirm that I've used o.parseHTML(text) correctly? This would still allow setting the raw HTML in html mode, but only because we haven't disallowed it. I updated the docs too.

Thanks!

[bevacqua]

See b3f2545