This is a port of MonoDevelop's MonoDevelop.Components.Docking library,
modified to be independent of MonoDevelop.

Original code from:
https://github.com/mono/monodevelop/tree/master/main/src/core/MonoDevelop.Ide

Commit: fb49f5b17bced266244831c07c28f9fc93915cb1

The public namespace has been change to Pinta.Docking to denote how much the
library has diverged from the source to get it working outside MonoDevelop.