Ensure auto_env_var_prefix converts dash to underscore like ArgParse

[helgi]

From https://docs.python.org/dev/library/argparse.html#dest: Any internal - characters will be converted to _ characters to make sure the string is a valid attribute name

Also bumped the version to 0.10.0 to be more semvar since 0.9.4 was really feature addition.

[bw2]

Hi @helgi I'm hesitating to merge this because there are many special characters that can't be included in auto_env_var_prefix (eg. '=', etc.), so I'd rather just leave it to the user to provide a sensible auto_env_var_prefix value instead of trying to fix specific kinds of bad characters like '-' .

[helgi]

This actually has nothing to do with the prefix it self but rather the arguments themselves. It is transforming --foo-bar with a HELLO_ prefix to HELLO_FOO_BAR instead of being saved as HELLO_FOO-BAR.

Right now the code in master straight up takes the config name, no transformation.

Replacing - with _ follows the argparse convention (linked to above) and also makes it possible for people to set ENV Vars that are separated with - in the config args.

export HELLO_FOO-BAR=100
-bash: export: `HELLO_FOO-BAR=100': not a valid identifier

Shell doesn't like the - it seems.

[bw2]

Oh, I see. My mistake.
Thanks for the pull request!

[helgi]

Thanks for merging! I can see why it would be confusing given people can add in their own prefix ending and I didn't specifically mention values only :-)

For a few minutes I did think about potentially just auto adding _ between prefix and the value as well but some people might not want any _ so I left that alone.

[torrance]

Does it make sense to do the same for all configuration sources, except the command line?

For example, I would expect p.add_arguments('-c', '--config-file') to have a corresponding yaml key of 'config_file'.