Enable all features by default in minijinja-cli

[KonishchevDmitry]

The doc says that all features are enabled by default, but it's not true: by default (and in the release binaries too) ini format support and shell completion aren't enabled + ini format is actually partially broken even when enabled (can't be specified in the command line).

This PR fixes the issue.

[KonishchevDmitry]

@mitsuhiko, I've actually faced with yet another problem with ini format. I have a *.conf file which I use in both shell scripts and for template generation. And in this file all variables are uppercase (as it often used in *.env files). But minijinja-cli loads them in lowercase, which was unexpected for me.

Is it intentional? Personally, I would prefer that my variables are passed as-is to the templates. It can be fixed by using configparser::ini::Ini::new_cs() instead of configparser::ini::Ini::new(). I haven't done this in this PR, but can add the change if you don't mind. At least it would be consistent with --env option, which passes environment variables as-is.

[mitsuhiko]

Yes, this should be fixed. Definitely unexpected and unintended. Could you also add a test for that?