Issue #13709: some fixes to the ctypes documentation. In addition to fixing

Issue #13709: some fixes to the ctypes documentation. In addition to fixing
the problems pointed in the issue, I removed the confusing Windows/Linux
distinction. It serves no real goal in the documentation, and is probably
wrong anyway since for Windows the WINFUNCTYPE constructor should be used.
In addition, the "look, this is faster on Linux" comment is misleading since
it's not explained. The outcome may just be an artifact of qsort implementation
for this particular input, and may change between C runtime version releases.