class ChunkRange

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Cord::ChunkRange

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`ChunkRange` is a helper class for iterating over the chunks of the `Cord`,

producing an iterator which can be used within a range-based for loop.

Construction of a `ChunkRange` will return an iterator pointing to the

first chunk of the Cord. Generally, do not construct a `ChunkRange`

directly; instead, prefer to use the `Cord::Chunks()` method.

Implementation note: `ChunkRange` is simply a convenience wrapper over

`Cord::chunk_begin()` and `Cord::chunk_end()`.