Add branching capability to MeshpyNetwork

[jameshalgren]

No description provided.

[jameshalgren]

Requires some sort of framework for a) holding the network; and b) intelligently traversing the network.

[jameshalgren]

(This is all Graph theory ... working on making sure the basic principles of that science are incorporated in our solutions to these prompts here.)

Ultimately, the network framework needs to support identification of the independent supernetworks, then support the concept of traversing all or portions of the supernetworks with a designation of the traversal method (i.e., hydraulic routing method) for each reach. We do not presently contemplate supporting segment-based routing method selection.

Need to be able to

1. Provide a list/count of all terminal nodes (downstream outlets with no further downstream channel)
2. provide a list/count of all terminal leaves of the network (hydrologic headwaters) with an association to the corresponding terminal nodes at the downstream end
3. identify the subset of reaches that are junctions -- index these.
4. assign weights to branches based on segment count, weighted segment count (e.g., length, local contributing area, or conveyance), junction count (stream-order), weighted junction count (e.g., contributing area).

Combined with the ability to subset a network above a given node or to count into the network from a leaf a certain distance, then subset back up, those same functions should provide the same capabilities for supernetwork subsets (i.e., Missouri River within the Mississippi basin, etc.)