[FeatureRequest] Imprement Download Feature

[turtton]

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その機能がほしくなった理由(こういう時に不便など)

This feature required by some services which cannot be supported stream mode(like niconico).

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追加してほしい機能についての説明

SSIA

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上の方法以外の代替案があればここに

Supports stream mode in all services. But I do not know the way to do this.

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追加で書きたいことがあればここに

This issue is related #65