keywords not being changed in model declaration function code

[paciorek]

We are not changing keywords (such as chol -> nChol) when compiling models.

This is because of the value of control$changeKeywords in NF_InternalsClass$initialize, which traces back to changeKeywords = is.null(compileInfo$C_fun) in nFunction() where this is a comment "by default, if C_fun is provided, don't change it, but user can override".

@perrydv : Shall I simply override this by modifying the control argument when we call nFunction from make_decl_method_nFxn?

[paciorek]

I've made this change in nimbleModel.