Documentation

- completed Documentation
- marked private methods with _
Adding support for more units than px

- Parameter for size now can theoretically be of any CSS-unit [BUT %
(will not be visible -> probably because of missing underlying element
with a set size )]
- introduced attributes to Pie which get their value at creation of the
instance through anonymous functions using parameter sizeString
- introduced methods to get sizeUnit, size  and sizeString from
Pie-Object
- modified methods createSliceFill and createSliceMask to use sizes unit
dynamically from the object