Also added new librsvg functions, and ignore deprecation warnings on new versions of librsvg. Disable sccache on FreeBSD.
- use sccache for build caching - add coverage reports as build artifacts - add lcov-summary for coverage summary - clean up/refactor CI yaml This resolves the FreeBSD part of #754.
Adding: - clang-8 - gcc-5 through gcc-8 - fedora & centos builds Fixing: - mysqlclient default search path - build on centos6
