Next generation of raster.gs

## Changelog
### 2.0.0
* mixin `grid` is now `raster`
* introduced `$quiet` mode
* prefixed private functions with underscore
* improved documentation
    - docblock documentation
* testing
    - input validation and error messages
    - bootcamp unit testing
    - continuous integration with travis ci
    - css linting
* concatenated main file for bower
* extracted functions in partials
* improved performance
    - cleaner code
    - clever use of placeholders