Create destination directory for LocalAsset copy / write if it does not exist

[Tyrannican]

When using Asset::copy("legit-src", "non-existant-destination") or asset.write("non-existant-destination"), the call will raise an error if the destination path does not exist for a LocalAsset.

Potential solution would be to check if the destination Path is a valid directory and create it (plus any parent directories) if not using something like fs::create_dir_all before the complete destination path (including filename) is built.
e.g.

let dest_path = Path::new(dest_dir);
if !dest_path.is_dir() {
    std::fs::create_dir_all(dest_path)?;
}

If this is intended behaviour then feel free to ignore this!

[ashleygwilliams]

hey @Tyrannican ! thanks for filing, this is actually a feature we need for our project oranda and so i'll likely implement something like this for 0.2.0 (about to cut a 0.1.0 right now)

i suspect instead of modifying the current function i'll probably build a write_all function that will create the dir if it doesn't exist. (oranda needs a few dir functions that you can see on the tracker :) )

[Tyrannican]

Sounds good!

Love the project, keep up the amazing work!

[shadows-withal]

Coincidentally, I think this'll be closed via #38.