Allow single data values per month to be used for calculating certain indices.

Recent testing revealed that this should already be configurable via the `max.missing.days` slot. 
Explore setting [max.missing.days](https://github.com/pacificclimate/climdex.pcic/blob/420db457cba091e289e66f7c2dfc6a5632f41471/R/climdexInput_class.R#L42C1-L51C33) to `date.factor length -1`. 