Fuxictr

+ [Feature] Add more models of year 2021-2022.
+ [Feature] Add tensorflow backbone support
+ [Refactor] Refine code structure to support model development with minimal code

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+ [Fix] Fix bug in EDCN ([29](https://github.com/reczoo/FuxiCTR/issues/29))
+ [Fix] Fix MultiHeadAttention bug ([30](https://github.com/reczoo/FuxiCTR/issues/30))

+ [Fix] Fix layernorm bug in MaskNet
+ [Doc] Refine demos and docs

+ [Feature] Add DSSM/DLRM/EDCN/AOANet/SAM models

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+ [Feature] Add DESTINE/MaskNet models
+ [Feature] Add support for default FeatureEncoder on new datasets