Fix bug in bounded int/float logic.
remove cython extension.

Now in cython package itself, as stable.
remove Cython Built-in extension notebook
remove more ref to cythonmagic
use Cython.load_ipython_ext to simplify
add whatsnew and uppercase C in load_ext

Use uppercase as this is what is in cython docs.
Added test
Use contentEditable to allow modification via the the slider readout
Add support to the float slider
Add keydown listener to commit changes on <enter>
Ignore the event object for handleTextChange
Add support for parsing pairs of numbers for range sliders
Change _parse_text_input to _parse_value and update float range regex
Fix infinite loop typo
Fix notify_trait getting called too early.
Require base/js/keyboard and use keycode.enter
forcing value to be in values
finish removing DelayedCallback from engine start

fix in #6608 was incomplete
fixed ls_alias for OpenBSD as it lacks the -G switch
fix ls_alias for NetBSD as well