fill in missing documentation details

[CeresBarros]

Many TODO's still left in documentation sections. @kdaust I've reached the limits of my knowledge and will need your input to fill these in

[cmahony]

@kdaust i'm also happy to fill out any you'd rather leave to me.

[CeresBarros]

@cmahony, @kdaust, when you get to this, could you do the following in this order:

1. looking at exported functions (Ctrl+Shift+F -> "@export" ) and revising all their documentation and filling in any gaps.
2. if you have time, do the same for non-exported functions that have documentation files (i.e. that DO NOT have "@noRd")
3. finally, have a look at the remaining functions with "@noRd". I strive to document all my functions, regardless of their visibility to users -- makes continued development easier when developers change :)

[CeresBarros]

@cmahony, @kdaust, please see list bellow:

Functions urgently needing documentation -- please check @description and @details sections, complete and add them as necessary.

• [x] normal_input()
• [x] historic_input
• [x] historic_input_ts
• [x] gcm_input
• [x] gcm_ts_input
• [x] gcm_hist_input
• [x] downscale
• [x] climr_downscale
• [x] lapse_rate

[kdaust]

@cmahony can you start with lapse_rate, downscale and climr_downscale please?