fortranobject.c compiles now with PyPy

- Manually copy arr->dimensions into array arr_dims[].
- Replace PyArray_FromAny() by PyArray_FROM_OTF(), to avoid the need
  to create a PyArray_Descr instance.
- Replace PyArray_DescrFromType() to investigate element size by
  PyArray_SimpleNew() + PyArray_ITEMSIZE().
- Modify docstrings and error messages that output character codes
  arr->descr->type, which are impossible to get with PyPy.