[dyntill] Clarify / Improve what the daily max rate is

[akrherz]

When I started dynamic tillage/planting, I had a 10% number stuck in my head for the maximum per-HUC12 rate that tillage and planting could operate at on a daily scale. Looking at the code presently, it is set to 6% overall and 3% prior to 20 April. The 6% number was derived from a crude analysis of change in NASS planting progress divided by workable days for the week. After many weeks of messing around and looking at NASS comparisons, I surmise that:

• intuitively, tillage rates should be higher. Implements are bigger and sometimes faster than planting. Fewer logistics.
• planting rates, as a proxy to workability, urgency, labor available, "mud it in mentally", should like increase into the season and not be a static value.

As an initial ballpark guess into this, I am now testing

• Tillage rate increase to 10% all season
• Planting rate partitioned 3% prior to 20 April, 6% prior to 10 May, 10% after

I think this is defensible at the moment :)

[akrherz]

10% is proving to be too aggressive, backing off to 25%.