Updating project to Grunt 0.4.x workflow.

Closes #79
- Changed gruntfile to new naming convention for 0.4.x (Gruntfile.js)
- Upgraded grunt module to version 0.4.2
- Set grunt-mocha dependancy to ~0.4.7
- Added and substituted lint with grunt-contrib-jshint for better coverage
- Updated readme with test and grunt installation information
Fixed all jshint warnings in showdown source.

closes #80
- Fixed tabbing of showdown source
- Added proper comparison operators
- Added missing semicolons