Build libyaml as meson subproject
Build libyaml as meson subproject

If the development headers of libyaml is not installed on the os, use libyaml from the local subprojects.

At the time of writing there is a bug in the latest ubuntu packages, preventing libyaml from installing correctly, so adding it directly as a subproject is a simple fix.

libyaml is cmake, but meson can import it anyways. This may not last forever, since most systems should be able to have libyaml.

libcsp/libcsp,libcsp/libcsp