Change the input variable names

[robertsawko]

Sorry, @AlexSkillen this is going to be nitpick on the variable naming but I just lost some time having Uin rather than UIn so maybe it will be useful in some way. Firstly, I think that In suffix is not necessary. It is obvious that this the input or inlet value. I am happy to fix this and send you a PR, but my suggestions are:

• drop it completely: U and R
• retain more of the variable meaning: Umean and R?

[AlexSkillen]

<Umean | UMean | UIn> and <R | RIn> seems the best option to me (keep UIn even though it is not the best name, for backwards compatibility. But only refer to Umean in the docs going forwards.

What do you think?

[robertsawko]

Hmm... That would be nice, but is that possible in OpenFOAM? There's some support for regular expressions(?) in some dictionaries but I never looked at it. We could add it explictly though by finding the string that matches first.