Define format for agronomic events

[dlebauer]

For an idea of the information file may need to include see ccmmf/organization#49 (comment)

This file could have a structure similar to climate driver inputs: https://github.com/PecanProject/sipnet/blob/master/docs/sipnet_inputs_outputs.md#3-climate-driver-inputs

Except that each event type will have different parameters.

Perhaps it could be something like:

site year doy event_type event_parameter_1 ... event_parameter_2
0    1998 100 fertilizer urea 200
0    1998 100 tillage    disk 10
0    1998 100 planting   <pft_name>
0    1998 200 harvest    grain