* Introduce `patcher` package that contains such interfaces to be
implemented:
- `PatchApplier` - the main patching engine that merges the stream
of patches and the stream of original object payload divided by
ranges. The merged streams result is output to `ChunkedObjectWriter`;
- `RangeProvider` - provides the original object payload by ranges;
- `HeaderProvider` - provides the original object header.
* Introduce `patcher` that implements `PatchApplier`;
* Cover all possible cases with unit-tests.
Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>
