Add a loader for loading resources

[chaseastewart]

Maybe something like this

[jg-rp]

I like this one too. And I'm OK with adding the importlib.resources backport as a dependency.

[jg-rp]

I've gone ahead and merged PR #147, which implements PackageLoader (docs), named to be consistent with Jinja.

As well as a package name, PackageLoader accepts a package_path argument, being one or more paths to load templates from, relative to the package root. package_path defaults to "templates", so would need to be explicitly set to the empty string if loading templates from the package root.

[chaseastewart]

Looks good to me.

[jg-rp]

PackageLoader is available in Python Liquid version 1.11.0, now released.

docs, source