Relax Path parameter to impl AsRef<Path>

[soerenmeier]

When trying to store GptDisk in a struct which was created from a Path the following error occurs.

error[E0597]: `path` does not live long enough
   --> src/main.rs:240:10
    |
238 |           let disk = GptConfig::new()
    |  ____________________-
239 | |             .writable(false)
240 | |             .open(&path)?;
    | |___________________^^^^^- argument requires that `path` is borrowed for `'static`
    |                     |
    |                     borrowed value does not live long enough
...
243 |       }
    |       - `path` dropped here while still borrowed

Making GptDisk<'static> the return type fixes this.

Additionally i propose to update the parameter Path to also accept a str like the std library does.