Updated production release

This is the latest and greatest libsc. When in doubt, use this one. Regression/breakage is minimal.

We had previously not used the github release mechanisms but linked to tarballs from our website https://www.p4est.org/.

This is only the second time we create a github release, one year after the first attempt. The library .so version is 3:0:0.

Please see the release notes for details.

First time github release

We had previously not used the github release mechanisms but linked to tarballs from our website https://www.p4est.org/.

This is the first time we create a github release. The libtool API version is 2:0:0.