[rust] Better handling for gnirehtet.apk path

Currently it’d just execute adb install -r gnirehtet.apk in whatever dir user was.

Not only is that insecure, that also makes it impossible to be run from any location except same dir, and makes distribution impossible.

So, I have two suggestions:

• chdir to gnirehtet file location before running any commands
• provide a way to override the path (via environment variable for example)

[JuanPotato]

fn chdir_to_executable_dirname() -> bool {
    env::current_exe()
        .and_then(|exe| fs::canonicalize(exe.as_path()))
        .ok()
        .map_or(false, |real_exe| {
            real_exe
                .as_path()
                .parent()
                .map_or(false, |real_dir| env::set_current_dir(real_dir).is_ok())
        })
}

I’m sorry, I like chaining things.

[rom1v]

@SalvatoreT I just published a new release v1.5 with this change and the fix for #273.

Sorry for the delay. (I work on gnirehtet and scrcpy on my free time, and scrcpy has higher priority.)

I wanted to change other things in gnirehtet before the release (like automatically close gnirehtet on the device on disconnection, unless an option is passed), but I had no time to work on it, so I just published the current dev branch.