Release of 2.0 Long-Term-Stable

Release of 2.0 Long-Term-Stable

This is NNStreamer 2.0 Long-Term-Stable release.

2.0's main features after 1.8 release include:
- Edge-AI capability (among-device AI) with pub/sub and query. In 2.0, this capability is an initial release without performance optimizations or feature extensions. We will eventually implement the promised optimizations and extensions with later (2.1+) versions.
- Tensor stream types updated: flexible tensors and sparse tensors are now supported. Single-tensor (other/tensor) is being obsoleted. Please use other/tensors instead.
- New H/W accelerators and AI frameworks supported
- Tensor-converter/decoder with subplugins and custom functions
- New elements: Tensor-IF, Join, Tensor-crop, Tensor-rate

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>