Leona/doc v0.24

[MLIR] Enable Gather Op

Add nbench support for double buffering

Remove support for adjoints of nodes

Python capsules support for ngraph::Function

* Pad: add pad mode SYMMETRIC

* Style.

* Disable UT on unsupported backends.

* Make required numpy version explicit.

* Read setup requirements from requirements.txt

Restore DEFAULT_FLOAT_TOLERANCE_BITS logic in lrn, sigmoid, softmax. Should allow re-enabling PlaidML tests (#3277)

* Added rpath setting for PlaidML backend

* Fix colons

* Separate build and install rpath

* Explicitly set target properties