added more description to logging and a python example

[jlheflin]

Is this pull request associated with an issue(s)?
No

Description
Adds a Python example that shows the difference between severity outputs. Also expanded the docs a little bit to better explain this.

TODOs
Should be r2g after review.

[ryanmrichard]

It would also be good to have a C++ example. Without the C++ example, a reader may think that this is a Python-only feature.

[ryanmrichard]

Suggested change

	all logging statements set as trace and below are enabled if the severity of
	all logging statements with severity trace and above are enabled if the severity of

[ryanmrichard]

Please use literalinclude and ensure your code is tested. Please also explain what your code is showing (in your case, it illustrates the difference in output when using different severities).

[ryanmrichard]

This is not valid reST (the headers/underlines must be the same length as the title).

[jwaldrop107]

I honestly think explicitly stating all of these is redundant with the above explanation. I would only provide one explicit example of one of the intermediate values, probably either info or warn.