Update template for release notes and CHANGELOG with latest few summaries from ngraph releases repo (#2696)

* Update Release Notes for Github summaries, incorporate feedback from doc review, fix typos, etc

* Fix links

* Rename RCs on template

* PR reviews

* Remove trailing spaces and add clarification on Python API example

* Fix typo

* Cleaner API doc reference for compile call

* Add a useful table for nGraph namespaces

* Remove layout namespace

* Show exploding kernel problem on illustration like IEEE preso

* Add new Introduction section based on IEEE presentation and illustrations

* WIP changes to doc navigation

* Update illustrations

* Cleaner ToC

* Minor fixes to the theme and removing useless bower files

* Better captions

* Revise intro

* Latest

* Make framework support section be its own section

* More updates to backend support section and add a new cpp api

* add changes to section

* Update intro with better detail

* Rework intro with better detail on motivation

* Editing

* Update README with new contrib guide filename

* Add the illustration referred to RE MobileNet group convolution fusion

* Fix off-by-a-line emph on code description

* Fix off-by-a-line emph on code description

* editing docs

* more doc updates

* Cleanup theme, update backends for PlaidML, remove stale font

* Add PlaidML description and doc update that should have been added with PR 1888

* Add PlaidML description and doc update that should have been added with PR 1888

* Latest release doc updates

* Add PlaidML description and doc update for PR 1888
* Update glossary with tensor description and quantization def
* Refactor landpage with QuickStart guides
* Add better details about nGraph features and roadmap

* Placeholder detail for comparison section

* Add section link

* order sections alphabetically for now

* update compiler illustration

* Address feedback from doc review

* Update illustration wording

* Formatting and final edits

* keep tables consistent

* Clarify doc on bridge and compiler docs

* Clarify doc on bridge and compiler docs

* yay for more feedback and improvements

* edit with built doc

* Fix typo

* Another phase of PR review editing

* Final review comment resolved

* note grammatically-correct wording preferred as often as possible.

* First iteration of shared subgraphs with onnx doc

* Updte onnx wheel install instructions with latest ngraph-0.9.0 versioning

* Updte onnx wheel install instructions with latest ngraph-0.9.0 versioning

* Update section  on subgraphs and shared subgraph docs

* Finalize edit of mxnet tutorial given status of our PR

* Make sure latest conf py is being used

* Update to latest index

* Add link to design doc mentioned by Ashoke and update about for consistent headings

* Update with PR feedback

* Update with new pip install instructions

* add more testing

* Further feedback review included

* Improve descriptions, given the new pip pkg install options

* Add note to onnx_ssg_tutorial

* Links updated to latest correct url

* Improve docs for Beta

* Reorganize TOC

* Better org in sections

* Make heading style consistent across indexes

* Update intro to framework builders

* Update intro to framework builders

* Add feedback from reviewers

* Minor fixes to ToC and editing

* Add section on FMV for miscellaneous use cases

* Update notice on README

* Updte link to howto index

* fix typo

* fix note

* Update glossary