prevent recursively generated Cython utility code (i.e. used by other Cython utility code) from appearing multiple times in the output due to a different outer module scope

--HG--
rename : Cython/Utility/CFuncConvert.pyx => Cython/Utility/CConvert.pyx

Fix code-example syntax in documentation

The trailing ``::`` mean that the string ``:file:`volume.pxd`::`` was being treated as the code example and therefore ``cdef float cube(float)`` was simply indented as regular font.

"nogil" for C++ casts