Add cram scaffolding

[Ninjapouet]

Would be nice to add cram in squeletons which would generate the folowwing defaults per program package:

• tests/output-tests/XXX/cram.t/run.t
• tests/output-tests/XXX/dune

with

$ cat dune
(cram (deps %{bin:xxx}))

where XXX is the package's name and xxx its executable.

[lefessan]

Unfortunately, there is currently no way to specify a directory for a package outside of the package directory itself.

So, it would probably be stored as src/PACKAGE/test/cram.t/ instead.