Meap Help Messages

My command-line parsing library - meap - can now generate help messages such as this:

$ cargo run --example macro -- -h
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/examples/macro -h`
Usage: target/debug/examples/macro [OPTIONS] STRING [DURATION ...]

    STRING           a string
    [DURATION ...]

    [-i INT]
    [-f, --flag-with-a-really-long-name]
                flag with a really long name
    [-c ...]
    [-h, --help]                     print help message

This completes the minimal viable set of features for this library, so I did an initial release on Feature-wise, I still need to add default values for optional arguments. I also want to spend some time writing documentation and tests.