Added pkg-config file and .gitignore

[oxoocoffee]

I was trying to build mongo-c-driver 1.7.0 on Mac OS X and it was failing to detect since missing pc file

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[oxoocoffee]

I signed it!

[junghans]

I would really use include(GNUInstallDirs) and not hardcode lib.

[cmumford]

@googlebot rescan

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[lavoiesl]

Any update on this PR?

I’m unable to compile the snappy ruby gem on nix because it can't detect the correct paths. This would be fixed by having a pkg config file.

[pwnall]

We will not add pkg-config support for now.

We don't want to get into supporting individual package managers, because the C++ ecosystem hasn't converged into a single solution, and there are quite a few equally reasonable candidates. We can't justify the investment into supporting all the package managers, or into supporting a couple of package managers and trying to rationalize where we drew the line.

[lovesegfault]

@pwnall By now pkg-config is a crucial part of the C/++ ecosystem, in particular for developers downstream trying to build bindings or link snappy into their non-C/++ projects.

I ended up on this issue because I need to link snappy into a Rust binary and have to write special code only for snappy because it doesn't provide a pc file.

Given that the complexity cost of this change is very small (24 lines) I ask you to please reconsider this.