1 and 0 are valid values for boolean in yaml and env
Reindented file
Reindented file
Fixed indentation
Check names for sections and options in config.

Accepted characters in names for sections and options are all lowercase
characters as defined by islower(3), plus '-' and '_' (if they are not
the first nor the last character of the name).
Do not accept "-" in config names

Environment variables are only permitted with underscore
To improve robustness and clarity, only allow underscores and lowercase
characters in config names
Test reading variables with underscore from env