changes for notebook: custom_plan

As noted in #9

What is pycat?
What is "md" in the up_down_once() plan of the custom_plan notebook?
How is logging handled? How to get the logger object?
Use %pycat .logs/ipython_logger.log to see the log file. It is OS-independent.
Another suggestion: make adding log messages the 1st exercise item so all of the demos provide more feedback.
What is bps?
What is stage_sigs?
Use from inspect import signature to document the call signature of functions.
How is real-time plotting handled?
How to count against a monitor instead of time?
How is kind used?
Use %%time at the start of slow cells to show how long the execution took to complete.
How does the RE reset things if a scan is stopped early. How to configure reset/cleanup?

BCDA-APS / bluesky_training