add a cython version of the function memory monitor
update memory_on_functions to use the cython version when available
use the psutil 2.x api
add missing cython file
fix typo
update test for the `memory_on_functions` factory
Update function_memory_monitor.pyx
Update test_cfunction_memory_monitor.py
Merge pull request #56 from enthought/function-memory-cython-monitor

Function memory cython monitor