repocutter: Add pattern matching to filecopy, refs #412

In order to implement pattern matching in repocutter filecopy, I propose the changes in this merge request.

It consists of two commits:

• the first one changes the -f flag. I find this flag confusing because everywhere else, it is used for fixed pattern matching. Additionally, its behavior depends on whether a BASENAME argument is provided. Hence I replace it with a -n or -basename flag which switches between "looking at full paths" and "looking at basenames" regardless of whether we are targeting a specific source file. I edited the documentation for clarity.
• the second one adds pattern matching like in other repocutter functions, with the -f flag now providing fixed pattern matching.

Feel free to merge only one of the commits or directly a squashed version if it better suits your vision of how the tool should work. I can also amend this proposal as you prefer.