Add snowfall interpolation by closest 3 points.
Merge branch 'master' of https://github.com/dskippy/HowMuchSnow into fresh
Update fresh to continue issuing pull requests from changes in master.
Add straight dist function, fix bugs.

Interpolation of amount of snow over nearby points should now work.
Uses the linear distance function instead of the great arc distance
function because I found conflicting formulas for the latter and at
these distances it shouldn't matter.
manual merge of interpolate code