Make properties in ITag available in public-facing API

[Jeehut]

Fixes #10.

[waliid]

What do you think about keeping things private and adding a new API like:

func streams(withLessOrEqualResolution resolution: Int) -> [Stream] {
    filter { $0.itag.videoResolution ?? 0 <= resolution }
}

[Jeehut]

Not very flexible IMO. People might have much more complex logic than what I've done here.

[alexeichhorn]

I guess we can make these properties public since they are inside the itag property anyway. But please revert the innertube client type back to what it was. Putting web there just breaks other things.

[alexeichhorn]

What do you think about keeping things private and adding a new API like:

func streams(withLessOrEqualResolution resolution: Int) -> [Stream] {
    filter { $0.itag.videoResolution ?? 0 <= resolution }
}

And I like this kind of filter functions. Could still be helpful, since fiddeling inside itags is not that straight forward.

[Jeehut]

@alexeichhorn I need the .web for my use case. But I did that change in a separate commit, so If you just want the public API part only, simply cherry-pick d6fcd96 and close this PR. Or simply do the changes on your main branch, it's simply adding the public keyword at a few places. Should be easy to copy.