Add initial stub for WCFS program and tests.
WCFS functionality will be added step-by-step in follow-up commits.

Some preliminary history:

kirr/wendelin.core@0ae88a32       X .nxdtest: Verify Go bits with GOMAXPROCS=1,2,`nproc`
kirr/wendelin.core@23528eb4       X wcfs: make it to use go modules for dependencies