Expose variables & add the lookup function capability

[kdorheim]

Documentation changes & added a new capability, this PR does not change Hector output

This PR is somewhat miscellaneous but

• Updates the RF_ALBEDO name to be consistent with the output rename that was done in an early PR
• Exposes LUC_UPTAKE so that users can set these emissions using the R interface
• Cleans up and completes the units-table, note that the units table is not a comprehensive table of all hector output/input units but only the input variables that are commonly changed/set by users
• Add capability to generate a table of Hector functions & their string names as desired in #547

[kdorheim]

@leeyap it would be great to get your input on the getfxn function, is this helpful? Or would it be better for the function to return the actual function instead of the string function name?

@bpbond your input on getfxn would be much appreciated! Something I am not sure about is the naming of the function and the associated .R scripts, I settled on getfxn to be consistent with getunits but also think that fxn.R script is kinda vague so I am open to other naming suggestions 🤷‍♀️. In data-raw there is a TODO because there is some hard coding that I don't love, here are a few potential courses of action

1. leave it as it and punt to a later issue
2. remove the units column from the table
3. use a try catch to handle the helper functions and parameters that don't have units or dates
4. replace the data-raw/save-input-params.R with code so that the input table stays up to date with the package which would help with this issue

[bpbond]

Something I am not sure about is the naming of the function and the associated .R scripts, I settled on getfxn to be consistent with getunits but also think that fxn.R script is kinda vague so I am open to other naming suggestions 🤷‍♀️.

Hmm, I don't have an immediate better suggestion. It works.

In data-raw there is a TODO because there is some hard coding that I don't love, here are a few potential courses of action

I see the TODO and responded to it. How does that relate to your courses-of-action list? They seem to be concerned with units/dates (I'm a little unclear on what problem exactly).

[kdorheim]

I guess it would be nice to be able to the fxns table to generate the information in the output table see the vignette/articles/output.hml but that would be a bit more work I may open as a future development issue. Unless you and/or @leeyap have other concerns, then I think this PR can be merged

[bpbond]

That would be my vote. A table with all the names and strings is hugely helpful, even if then the users need to go check about the units, etc.

getfxn does need to be documented somewhere. Is a logical place in a vignette we could add it?

[leeyap]

@kdorheim this is super helpful! I think it makes sense to return the function as a string, what do you mean by "return the actual function?"

[bpbond]

Added @leeyap aș a formal reviewer, as I agree it'd be very useful to get her feedback.

[leeyap]

I agree that the table is very very useful, even without units since that's easy enough to check in R. Otherwise, no comments from me, thanks @kdorheim!

[kdorheim]

We could add a vignette, as of now though it is documented with rxoygen so help(getfxn) will generate documentation and it will automatically be added to the online pkgdown documentation. I've added an example code to that documentation. Do you still think we need a vignette?

[bpbond]

Not for now anyway, no. Good to go from my pov.