Do not try to load pygments if morse is not started with -c
[doc] Fix several spelling issues in user/basic_morse.rst

While here, deal with a few other styles issue

This page must probably be updated to reflect last changes in morse
(environment, options restricted to certain commands, ...) (Hi
Séverin).
[bin] Export the whole sys.path in PYTHONPATH to Blender

The sys.path is not initialized in the same way with the python3
interpreter, and the inner python3 embedded in blender. So export fully
the sys.path through PYTHONPATH so the user get the expected environment
in blender context.

It was done before, but lost in 987162b787. Reported by Felix Ruess.