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

early version of 60N boundary assessment report

updated boundary assessment code to use multires spline results

fixed critical typo in post-processing enblended layer

added GRASS commands to run terraflow on Canada boundary DEMs

added R code to create various boundary assessment figures