- geocoon description improvements
- library description improvements in the license header
- added information about OGC standard and Shapely API to the introduction
  chapter of the documentation
- added geocoon.factory module documentation
- major cleanup of documentation section describing data frame and series
  object creation
- cleanup of documentation section describing vectorized attribute access
  and method calls
- improvements to the split-apply-combine section of the documentation
- documentation cleanup of the design chapter
- code cleanup