Support for completions

[Jedsek]

Again :)

[Jedsek]

I help you reduce clap's feature, because crate_version! is just a simple macro:

#[cfg(feature = "cargo")]
#[macro_export]
macro_rules! crate_version {
    () => {
        env!("CARGO_PKG_VERSION")
    };
}

Just replace it by using env!

[Jedsek]

And now, no clippy warnings :)

[Jedsek]

Also, I changed the edition form 2018 to 2021 in Cargo.toml and it could be compiled successfully.

[bootandy]

Looks like the old 32 bit builds are broken. (i686) ( Could this be the change from 2018-> 2021 ? )

[bootandy]

I don't think its the edition change as I opened a separate PR for that: #249

[Jedsek]

I fix the max depth.
(I just thought about 64 bit before)

[Jedsek]

Because a proble of clap, we could't set the default value of depth (When use a function which return value is a Command, because lifetime, see clap-rs/clap#2150)

So I changed the build_cli's signature to accept a new argument: max_depth to avold this problem. Otherwise, I think I have to add a dependencies const_format to achieve the same purpose.

[Jedsek]

@bootandy All checks have passed, this pr could be merged