New features for web parameter parsing module

[namespacestd0]

1. Integrate OpenAPI spec generation with https://github.com/zcqian/biothings.api/blob/openapi/biothings/web/openapi/contexts.py
2. Support forgiving argument processing, for example, for a number limited to 1000, if it's larger than 1000, use 1000 instead of returning an error: Status code 400 (bad request) if more than 1000 IDs are posted to the chemical annotation service mychem.info#88
3. differentiate argument source, like path argument, body argument, query argument. It will be useful in: Handler for BioThings API providing graph type data pending.api#20

[namespacestd0]

additional possible features:

1. warn unexpected parameters
2. autosuggest similar names for bad parameters input