fix some bugs (shenweichen#185)

- fix bug in `get_varlen_pooling_list`
- fix bug in `SequencePoolingLayer` when `mode='max'`
- Add alias `ONN` for model `NFFM`

v0.7.1

* Simplify `VarLenSparseFeat`, support setting weight_normalization.

* Fix problem of embedding size of `SparseFeat` in `linear_feature_columns`.

refactor feature columns

refactor feature columns 
- different features can use different `embedding_dim`
-  group-wise interaction is available by setting `group_name`

no message

simplify input logic

Update index.rst

update for tensorflow2.0

Refactor input module of linear part

Add FiBiNET

Update interaction.py