miniz-sys: add support for using system-wide miniz

[ignatenkobrain]

In Fedora we unbundle all libraries and would like to not use bundled miniz.

There is no pkg-config, but simple #include <miniz.h> and -lminiz should work just fine.

[infinity0]

Alternatively, reimplement miniz in rust?

I see rustc already dropped miniz and there are a couple of alternatives:

https://github.com/alexchandel/miniz-rs
https://github.com/Frommi/miniz_oxide

The latter one even recreates the API of C-miniz.

[infinity0]

In Debian we just patch away miniz and miniz_oxide_c_api to use zlib instead.

I suggested #181 as an alternative; I don't see the value of including either miniz or miniz_oxide_c_api in Debian or anywhere else really, when pretty much all systems already have a zlib, especially in light of issues like #142.

[joshtriplett]

flate2 now defaults to miniz_oxide rather than miniz-sys, and if you can count on system libraries then you're more likely to have zlib than miniz. I don't think there's much value in supporting a system miniz; even the miniz-sys feature is more-or-less deprecated and only exists for compatibility.

I think this can probably be closed.