Started to work with mouse selection.
Started to work with mouse selection.
Continued adding mouse selection support.

Need to debug this in Windows machine, since the debugger
in MonoDevelop is no handling events well.
Got the mouse selection to work finally.

Need to add a lot of tests around SExprPath. That works
right now, but not sure how the corner cases are handled.

Also need to refactor the test program generation, and
think how the HitRects should be maintained in the
render process.