More extensive markdown support

Checklists and equations don't seem to be supported (I guess they are out of the standard md specs). I'd like to use cacher for my to-do lists and sciency stuff, so this would be a *great* addition for me. Thanks!

$-b \pm \sqrt{b^2 - 4ac} \over 2a$

- [x] Tables

- [ ] Checklists

- [ ] Equations