reconsider attributes

[yueyinqiu]

To support our attributes that could change the behavior of serialization, we are going to convert the object to a dictionary before passing to js layer.

However this will make things complex. For example #24 would happen as we may overlook some cases in new features. A more serious problem is that we can't save a big integer value for now, since it might be considered as a decimal value #32 (comment).

So I'm considering to remove those attributes. Instead, we could use JsonIgnore to ignore a property, and JsonPropertyName to change the column name.

I would try that soon and will create a PR if succeeded.