Enforce md style.

- multiple blank lines before header
- skip header level
- colon at end of header
- break long lines
- align definition like lists at marker
- case typos
- informal contraction `bio`

@randx: please watch for the header points which are mentioned at http://www.cirosantilli.com/markdown-styleguide/#headers. Please open PR if you wish to propose a change to the style.