renamed growpest to growpest-curr, Janssen version to growpest-janssen, and added a supposed function version of the latter.
additional notes on pest dispersal rates
comments, experiments commented out, text on UI
Finished testing alt versions of growpest

Finally figured out the correct way to test that the new
version matched Janssen's.  It does.  They are the same
but for very small float rounding.
Merge branch 'master' into growpest-compare