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

Update run_dsin.py

pull dev for v0.4.1

add DSIN
refactor layers