Feature request: exclude libraries from `auto_link` option by pattern.

[cessen]

I am using cargo-appimage to automatically package software in a CI pipeline. This makes it difficult to make manual by-hand interventions as described in the readme for e.g. excluding glibc from being bundled with the Appimage.

I think it's likely that the bundling of glibc and perhaps a couple of other libraries are resulting in a segfault on systems with an incompatible glibc version. Although I'm not totally sure, and will be investigating further.

Regardless, providing a way to specify in Cargo.toml what shared libraries to exclude from auto_linking (possibly via a regex pattern matched on the filepath) would be really useful, and eliminate the need for the awkward by-hand workflow outlined in the readme.

[cessen]

I've made a PR (#11) that implements this. I've tested on my CI pipeline, and it indeed allows me to fix the aforementioned segfault bug in my appimages by excluding glibc.