Add function config.is_true

This function will provide a common interface for determining truth, so
that module functions can properly determine the truthiness of a value
passed in via the CLI.

This will allow some code in the package providers to be a little less
ugly, and will also come in handy when #3363 is implemented.
docstring modifications to make docs look pretty
mode docstring tweaks
Merge pull request #4054 from terminalmage/issue2783

Add function config.is_true