Swap in structopt to get -h/--help

[scribe]

Add the short version of help by switching to structopt flag by switching the argument parsing to structopt to fix #30

[scribe]

I saw your post about hacktoberfest contributions being welcome. If this is in any way not ok please feel free to close right away.

[Tamschi]

I saw your post about hacktoberfest contributions being welcome. If this is in any way not ok please feel free to close right away.

It's looking great from the diff! Thank you!

I'll just run the checks and try it out. (If one of the checks fails it's likely my fault, I'll look into it in a moment.)

[Tamschi]

reserde on  structopt-for-h is 📦 v0.0.2 via 🦀 v1.55.0 
❯ cargo run -- -h
    Finished dev [unoptimized + debuginfo] target(s) in 0.66s
     Running `target\debug\reserde.exe -h`
reserde 0.0.2
Transcode a self-describing format into a different format.

Currently supports Bencode, Bincode (--out only), CBOR, JSON (--pretty), TAML (--in only), XML, x-www-form-urlencoded
(as urlencoded) and YAML. All names are lowercase.

USAGE:
    reserde.exe [FLAGS] [OPTIONS] --in <in-format> --out <out-format>

FLAGS:
        --enum-bools    case-insensitively convert unit variants with name `true` or `false` into booleans
    -h, --help          Prints help information
    -p                  pretty-print (where supported)
    -V, --version       Prints version information

OPTIONS:
        --if <in-file>        where to read input from. Defaults to stdin
    -i, --in <in-format>      what to read [possible values: bencode, cbor, json, taml, urlencoded, xml, yaml]
        --of <out-file>       where to write output to. Defaults to stdout
    -o, --out <out-format>    what to write [possible values: bencode, bincode, cbor, json, urlencoded, xml, yaml]
    -s <stringify>...         stringify bytes and non-string value keys into strings where possible, possible values
                              are: utf8. (Tries encodings in the order specified.) [try with: --in bencode]

Perfect, thank you!

It incidentally also improved the error output a bit, if you pass no parameters at all.
This should make it easier for new users to discover how to use the tool.

[Tamschi]

It's quite late here, so I won't release a new version right now, but I'll put it on my tasks list for tomorrow.

[Tamschi]

(I'm going to do a little repository gardening and assign you to both the original issue and this PR too, but there's no further action needed here.
Edit: Interesting, I can't assign you to the issue since you didn't comment there. I'll leave it as-in in that case.)