Explore deleting rl.exe

The folder `bin/rl` contains source and build files for rl.exe this is a windows only test runner application, it is currently built and used by the CI on windows.

BUT I can't see anything it does that `test/runtests.py` can't do.

Unless anyone has an objection?
We should:
1. [x] update `test/runtests.py` to be fully functional on windows (if it isn't)
2. [x] update `test/jenkins.testone.cmd` to call runtests.py instead of `runtests.cmd`
3. [ ] Delete `runtests.cmd` (wrapper script around rl.exe)
4. [ ] Delete `bin/rl` and all references to it

The one key reason I could see not to do this is if `rl.exe` is significantly faster than `runtests.py` (if so we should contemplate getting rid of `runtests.py` instead though that would be more work) - best way I can see to test this is to update `runtests.py` to handle windows then change the CI to run on it and see what happens.