Used pattern matching to match subcommands

[vedangj044]

Fixes #3

• The panic caused by unwraps is handling using pattern matching.
• required(true) is added to app_id_arg to delegate error handling to clap.

[vedangj044]

The following things can be improved in this PR, need your suggestions

• The matches.subcommand() returns (&str, <options>), can we convert enums to string. I was not able to use Verbs::create.as_ref() or format!(Verbs::create.as_ref()) as a match expression.
• Use of enums is a discussed issue in the clap repository as well, maybe we can implement this in the future. See here.

[jbtrystram]

The following things can be improved in this PR, need your suggestions

* The `matches.subcommand()` returns `(&str, <options>)`, can we convert enums to string. I was not able to use `Verbs::create.as_ref()` or `format!(Verbs::create.as_ref())` as a match expression.

* Use of enums is a discussed issue in the clap repository as well, maybe we can implement this in the future. [See here.](https://github.com/clap-rs/clap/issues/459)

clap-rs/clap#1104 this issue seems to be stalled for a few years now, so i would not count on it ! It's nice if it finally lands, but in the meantime i'd like to keep the enums and find a workaround.

[vedangj044]

Actually, that issue was the first time they discussed it, they have added an example about the use of enums here. Our current implementation is good too, so I think we keep it this way for now.

[jbtrystram]

Can you explain a bit more the issue you have with matching the commands with the enums variants ?

[jbtrystram]

I already used drang for converting the enums variants to string. Maybe you just need to import asRefStr in the main file and use it ?
https://docs.rs/strum/0.20.0/strum/derive.AsRefStr.html

[jbtrystram]

See comments. Also please run cargo fmt on your PRs

[jbtrystram]

Why not adding : setting(AppSettings::SubcommandRequiredElseHelp) to the App object at the root level instead of adding it to every subcommand ?
(maybe it does not works recursively, but i think it does at it is not mentionned in the documentation)

[vedangj044]

Tried this but it doesn't work recursively.