mra_rom_check.sh outputs so many errors that most people don't use it

I have worked on cleaning up most of the MRA files in the MiSTer-devel repositories in December 2020, but certain types of issues required script updates.

1. Errors beyond one screenful were not traceable
   -> In pull request 46, this is fixed by outputting to a logfile

2. "No MAME version" dwarfs other issues, and it is not clear where this information comes from (and it does not affect operation)
   -> This outputs to a separate logfile and is no longer directed to the screen because of the number of these issues, particularly in the Jotego MRAs, which most people have on their system. In order to make the script useable, follow-ups to Jotego's repos will also be necessary, so that this error can be re-enabled in future when it can be meaningful.

3. Changes to how ZIP file and CRC errors are being identified, to reduce false positives.
   -> This was done by @alanswx , and put in pull request 48 (which is also now integrated into pull request 46)

Start with mra_rom_check.sh and review pull requests 46 and 48, which the issue identifies as covering the proposed changes. Check whether the script now keeps excessive errors traceable, separates the "No MAME version" output, and reduces ZIP/CRC false positives; completion would require those behaviors to be present and usable.