Update format of changes.txt to markdown
Update format of changes.txt to markdown

Shortens the file a bit and streamlines with the CHANGELOG.md in MR2.

De-shortlinked the link to the full changelog as this is more friendly
to users. Who likes to click bit.ly links when there is a clean link to
a Github wiki page?

tkn98/n98-magerun,pocallaghan/n98-magerun,tkn98/n98-magerun,pocallaghan/n98-magerun,tkn98/n98-magerun,pocallaghan/n98-magerun