Added ability to have equidistant nested column gutters.
Removed requirement of specifying the number of nested columns, you
set a nested flag to true or false instead.
Condensed the numerator and denominator into a single argument called
ratio. Col can be called like this now: col(1/4) or col(0.25)
Added the parent_ratio argument, this is necessary for the equidistant
gutters.
Altered the way the get function is calculated. col, span and offset
now all call the get function for their calculations.