more boundary analysis updates, especially discussion of stats

added correlations/RMSE discussion, plus many new edits

numerous changes and revisions to boundary assessment doc

switched plot to bin by SRTM elev rather than ASTER

added ASTER vs SRTM elevation comparision plots

revamped aspect/flowdir boundary assessments to use circular statistics

split the dem-fusion code snippets into separate script files

minor cleanup of code comments

added multiresolution spline fused layer as terraflow input

added prose text to boundary document, and (partly) refactored figures