returned Datetime type for proton datetime and datetime64

[leo-cai-timeplus]

similar to #38

• returned Datetime type for proton datetime and datetime64
• implement json.Marshaler, json.Unmarshaler, yaml.Marshaler, yaml.Unmarshaler interface for types.Date and types.Datetime

[qijun-niu-timeplus]

I think it's a breaking change. Why do we do this?
Is there a issue about this PR? What's the context of it?

[qijun-niu-timeplus]

If we have to make this change, @ye11ow could you please help to estimate the influence to neutron?

[leo-cai-timeplus]

This pr can make it easier for user to read data from proton, then marshal data they read to json in the same format as proton do.

Run select * from example format JSONEachRow with proton client, the col whose type is datetime is in format of 1970-01-01 00:00:00. However, if user read the col via proton go driver, they will get a value whose type is time.Time. Using encoding/json to marshal time.Time and the format will be like 2006-01-02T15:04:05Z07:00.

Type datetime and time.Time can easily be solved, but if user want complex type for example map(string,array(array(map(string,datetime)))), to marshal all time.Time with format 1970-01-01 00:00:00 will not be easy.

[leo-cai-timeplus]

This pr is of low priority