pugs

This is just a test to plug builtin-functions into the language.
One can write
``
m1 = transform(m0, f);
``
where `m0` and `m1` are meshes (m0 being initialized) and `f` is a function.

By now the function is not used, its type is not checked the only validated info
is that it is actually a function...

For validation purpose, one distorts the mesh using a C++ code.