Simplify compression when rebuilding the apt repo

[PeterJCLaw]

As pointed out by @kierdavis in #22 (comment), python has an lzma module which provides xz compression meaning that we don't need to call out to another process for this.

[kierdavis]

Changes appear fine to me. I'll aim to give this a test on monday evening.

[PeterJCLaw]

There's a bunch of changes I've made to this repo recently which I don't think have been tested; I'll test that this still works shortly.

Do we have guidance on what/how to test runusb anywhere? (If not, I'll make some)

[kierdavis]

There's a bunch of changes I've made to this repo recently which I don't think have been tested; I'll test that this still works shortly.

In that case I won't worry too much about testing this before merging it. It's occurred to me that we ought to have a stable branch in addition to master, or a stable master and unstable devel - anything that separates versions of repos that have been practically tested from those that haven't.

Do we have guidance on what/how to test runusb anywhere? (If not, I'll make some)

Not that I know of. I was just going to check if doing updates still works, but some notes on how one should test runusb would be useful (for future as well as for now).

[PeterJCLaw]

I'd rather not get into stable vs develop etc. as it greatly complicates things. If we're going to have a testing phase we should expect that that passes before merging into master. We should also automated them...

I'll merge this shortly then create some tests.

[PeterJCLaw]

(incidentally python/typeshed#1844 will add support for lzma in the typeshed)