* Written the draft of the specification of the operation RFFT.
* Started to write the specification of the operation IRFFT.
* Small fix.
* Renamed RFFT operation as RDFT.
* Fix in Operations_specifications.md.
* Written the specification of the operation IRDFT.
* Fixes in examples.
* Fixes in opset9.md and Operations_specifications.md.
* Small fix.
* Replaced opset8 by opset9 in opset9.md.
* Deleted redundant sentences.
* Small fix.
* Replaced input_shape by data_shape.
* Fixed mistypes.
* Fixes of mistypes.
* Fixed typo.
* Fixed RDFT specification, in order to perform signal_size input as in TF and PyTorch.
* Fixes in examples for RDFT.
* Fixes in the output shape calculation of IRDFT. Now this calculation is as in TF and PyTorch.
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