Add Lisp support for fenced code blocks

Fixes #156
Improve README
Add missing header to changelog
Command to convert SETEXT headers to ATX
Merge pull request #163 from bordaigorl/setext2atx

Command to convert SETEXT headers to ATX
Improve changelog
Fix a small bug in macro
Merge pull request #157 from SublimeText-Markdown/v2.0.7

Version 2.0.7