Pkgconfig

[mattip]

Add a pkgconfig file to the tarballs. Fixes #74. Note that updating the submodule to OpenBLAS 0.3.20 does not update the built OpenBLAS to 0.3.20, it just makes local developement easier.

[mattip]

The openblas.pc file assumes the tarball will be unpacked into C:\opt on windows and /usr/local otherwise. We should document the need to set PKG_CONFIG_PATH to find it. Also, local builds will prefer to set PKG_CONFIG_SYSROOT_DIR since they may not be able to unpack into those locations.

[mattip]

@rgommers: do you want this for the current OpenBLAS release? If I merge this it will overwrite the existing files.

[matthew-brett]

Do all the binaries work? If so - then yes, let's use them.

[mattip]

gahh, the uploaded file name doesn't have the version anymore it is `openblas64_--manylinux2014_x86_64.tar.gz

[mattip]

fatal: unsafe repository ('/io/OpenBLAS' is owned by someone else)