Some more user-friendly APIs

[Tiiiger]

There are many potential ways to do quantization for a neural network, for example, different bits for forward and backward, different number type for forward and backward. However, sometimes we also prefer simple quantization. We should add APIs to support:

• pass in 1 set of argument and use it for both forward and backward
• use 1 argument to change all number types for WAGEM, use 1 argument to change all rounding scheme for WAGEM.
• change argument to take number format object instead.