Need to consider min/max values in functions

[StaceyFisher]

Derived variables do not consider out of range - for example BMI can output a negative value, or value outside of max/min

[StaceyFisher]

Consider having default min/max values in the function, which can be overridden by min/max in the variable_details sheet

[DougManuel]

@StaceyFisher @caitlink12 and I wondered about using recStart and recEnd to identify out-of-range and other errors in derived variables.

For BMI, if the allowable range is 18 to 45, then recStart = [18, 45], recEnd = copy. Else NA(a).

[DougManuel]

This is being implemented in v3.0.0