Added roof command line option
[Fixes #5] Created a roof_geometry data structure and code to create and manage the roof geometries.
[Fixes #5] Implemented a generic search algorithm with callback mechanism for determining hits. Adds found pixels patches as adjacencies to the roof patches.
[fixes #8] Changed the code to create two flow tables, subsurface and surface. Roofs are only treated in the surface flow table.
Merge of the readroof branch