Enforce that options must be used by command before matching a subcommand

[natecook1000]

We were incorrectly skipping over dash-prefixed inputs when looking for the next
subcommand. This means that input like command sub1 --foo sub2 would match the
sub1 and sub2 subcommands, even if --foo wasn't defined by sub1. This manifested
in issues where a value expected by --foo would be eaten by the subcommand matcher.

Note that this changes a couple test fixtures where we were incorrectly specifying inputs.

Fixes #92.

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary