Reducing the dependency footprint

[scarytom]

I'm using nippy without any compression. It would be nice to exclude the dependencies that are (I think) only required for compression, and keep the dependency footprint smaller. At the moment, if I exclude these dependencies, then compilation fails. I guess the code could be re-worked to dynamically reference classes in these libs? Happy to experiment with this and do a pull request if you think it is acceptable to do this.

nippy/project.clj

Lines 13 to 14 in 5a9a391

	[org.tukaani/xz "1.9"]
	[io.airlift/aircompressor "0.27"]]

[ptaoussanis]

@scarytom Hi Tom! Would be happy to look at a PR that makes these optional if it's pretty simple and doesn't negatively impact current users 👍

[scarytom]

I quickly put a pull-request together, just to show you what it would look like before refining anything too much. I'm concerned that these changes might affect performance, which is obviously a big deal, so benchmarking definitely required.