pyhelper: Add ability to route error messages to python logging

Instead of writing error messages to stderr, route them into the
python code and use the standard python logging system.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/Installation.md

@@ -129,7 +129,7 @@ The host software is executed by running the following as the regular
 "pi" user:
 
 ```
-~/klippy-env/bin/python ~/klipper/klippy/klippy.py ~/printer.cfg -l /tmp/klippy.log < /dev/null > /tmp/klippy-errors.log 2>&1 &
+~/klippy-env/bin/python ~/klipper/klippy/klippy.py ~/printer.cfg -l /tmp/klippy.log < /dev/null > /dev/null 2>&1 &
 ```
 
 Once Klippy is running, use a web-browser and navigate to the

docs/Todo.md

@@ -51,8 +51,6 @@ Host user interaction
 
 * Improve logging:
 
- * Route errors from the host C code to the main log file.
-
  * Automatically roll Klippy log files. The default log file should
    have the current date in the log file name.