Improve qsc encoder integration

[baentsch]

Build time for oqs-provider significantly deteriorated when qsc-encoder integration was done. A glance at disk usage shows the problem vividly: The src of qsc-encoder is more than 2x as large as all of OpenSSL, 3x the size of a fully built liboqs and thus roughly 60% of a complete oqs-provider build (incl. opensslv3 binaries and libraries):

--> Is it really necessary to add KATs for all algorithms (again)? That alone seems to be 255MBytes. Then there's PPTX files and huge .git index files: The latter are 38x larger in qsc-encoder than in all of oqs-provider (3.5MB vs 138MB).

@bhess: Do you agree that this is not OK and have time to remedy this?

[bhess]

Yes the repo was quite large due to the KAT and unrelated files. I now created a separate smaller repository containing only the library. See PR #131.