support cargo's --manifest-path

[PhilippMolitor]

self-explanatory. issue raised in #95

[burrbull]

Could you fix CI/clippy errors?

[jannic]

Could you fix CI/clippy errors?

The clippy warning is not related to this change. Just a new warning on nightly.

https://github.com/rust-embedded/cargo-binutils/pull/148/files

[PhilippMolitor]

Correct, I think none of the failing CI scripts have to do with my changes. I built and installed this on my machine on latest rust stable without any issues.

One more comment because i noticed it with my current work that uses cargo-binutils:
Some of the flags that are re-implemented from cargo, like --release and --no-default-features are not implemented correctly, they still require a value instead of just working as a flag.
With clap, the Arg builder needs this additional setting: .action(ArgAction::SetTrue), and it also should be retrieved as a flag instead of a normal .get_one() parameter.
The current workaround is to pass --some-cargo-flag true (or any other value).

[Emilgardis]

can you please remove the merge commit? same goes for the other prs