[R] broke code out into individual files (fixes #243)

[jameslamb]

Per #243, in this PR I propose breaking out classes and functions into individual script files. This can make the code a little easier to navigate and diffs in PRs easier to read.

[StrikerRUS]

One minor note from my side.
I suppose that NEWS should be updated. Right, @mlampros ?

[jameslamb]

it depends on the purpose of NEWS.md. This is not a user-facing change (i.e. no one who installs that package has to care about it).

[StrikerRUS]

@jameslamb That's true. Leaving the decision for @mlampros, since he is the maintainer of R-package.

[mlampros]

From the perspective of a user the only case that I can think, is when someone intends to search for a code snippet in the files. Previously, for instance I had to search in 3 files whereas now in multiple. On the other hand if someone intends to use the functions of the package (after installation) then he/she will not see any difference at all. I mostly write such changes in the NEWS.md file, but I guess, now I'm not the only contributor for the R package in the RGF-team repository.

[jameslamb]

IMHO a non-developer "user" doesn't need to ever look at scripts or search through them, since you can always run a function without parentheses in R and see the source code printed in the console.

Either way, if you tell me to update NEWS I'll update it!

[mlampros]

It depends. When I started learning R I didn't know that I was able to run a function without parentheses, as you said, so that I can have a look to the code. Moreover, I think it's also a matter of preference. Some people prefer to view the code in the files directly (like myself) and others don't.
I would suggest that we add this change in NEWS.md file, if you don't have anything against.

[jameslamb]

Makes sense to me! I just added the update to NEWS.md

[mlampros]

thanks

[StrikerRUS]

Thanks a lot for your contribution!