Progress indicator for cythonize()

[jdemeyer]

Implement a simple progress indicator for cythonize():

[  1/411] Cythonizing sage/algebras/letterplace/free_algebra_element_letterplace.pyx
[  3/411] Cythonizing sage/algebras/letterplace/letterplace_ideal.pyx
[  4/411] Cythonizing sage/algebras/quatalg/quaternion_algebra_cython.pyx
[  2/411] Cythonizing sage/algebras/letterplace/free_algebra_letterplace.pyx
[  6/411] Cythonizing sage/calculus/interpolators.pyx
[  7/411] Cythonizing sage/calculus/riemann.pyx
[  8/411] Cythonizing sage/calculus/var.pyx
[  5/411] Cythonizing sage/algebras/quatalg/quaternion_algebra_element.pyx
[  9/411] Cythonizing sage/categories/action.pyx
[ 10/411] Cythonizing sage/categories/category_cy_helper.pyx
warning: sage/misc/classcall_metaclass.pxd:9:4: type already a builtin Cython type
warning: sage/misc/nested_class.pxd:2:4: type already a builtin Cython type
[ 11/411] Cythonizing sage/categories/category_singleton.pyx
[ 12/411] Cythonizing sage/categories/examples/semigroups_cython.pyx
[ 13/411] Cythonizing sage/categories/functor.pyx
[ 14/411] Cythonizing sage/categories/map.pyx
[ 15/411] Cythonizing sage/categories/morphism.pyx
...

[scoder]

thanks!