Slackdown

- Added support for hyperlinks.
- Plain links will be rendered inside `<a>` tags with its contents as both the `href` and `innerHTML`.
- Named links will be rendered inside `<a>` tags with its name as the `innerHTML` and its link as the `href`.
- References to other users will have their hyperlinks removed.
- References to other channels will have their hyperlinks removed.
- A new method `parse` was added. Currently, it takes an object with a `text` attribute and renders it. This is in preparation for more complex parsing which requires more than just the Slack text, but the entire Slack message object.
- Other minor bug fixes.

- All elements should now be wrapped inside proper block elements like `<p>` tags.
- Formatting characters inside of `<pre>` elements will now be rendered as they appear instead of formatting the text around them.
- Fixed a major bug in which combining list delaminations in a single list resulted in malformed lists.
- Added more comprehensive tests.
- Added preliminary support for escaping. See [this issue](https://github.com/datadesk/slackdown/issues/9) for more.
- Other minor improvements.

Initial release