Update of gitignore to exclude output files

[seanfuture]

Open to suggestions as to how to best handle - thanks

[samnazarko]

Hi

Thanks for the PR.

You should squash the merge commit.

I've seen a couple of your comments on GitHub and it looks like you might be interested in contributing to OSMC. If that's the case, let me know. There's a lot of low hanging fruit in the build system, but time pushes things back, particularly when the benefits are not always seen by our users.

Looking at my notes from September, some thoughts I had:

• Create a topic branch called better-clean-rules
• Instead of kerfuffle where do use sed rules to clean up Debian packages, we could use git checkout on specific files we modify. These changes would be in build.sh. This would work for Makefile and JSON files with a clean rule as well.
• Introduce pre-commit hooks that call this make clean rule. This can be done for the current working directory if we assume that our developers only commit in the directory that they are in.

This is a bit loose, and there's plenty to be fleshed out, but happy to elaborate and discuss if you want to work on this.