fixed single column width
bootstrap demo included
cleaned up the whole system
* $gutter default is now 4 (was 2 before)
* replaced $quiet mode with column mixins
* removed `first` helper
* cleaned the code up
* introduced configuration objects
* create percentage based ratios (was factor based before)
* fixed width bug with combined columns
* splitted code in private and public parts
* included pad classes
* `.grid-row` is now `.raster`
* added some demos