use pointer instead of int

[zetaab]

according this https://stackoverflow.com/questions/38486564/golang-unmarshal-marshal-json-with-int-set-to-0-does-not-seem-to-work we should use *int instead of int if we want marshal 0 value.

fixes #74

[jeremyjacob]

This would greatly increase development velocity. Any ideas on where to start with a PR?

[hanayashiki]

maybe they haven't started to write a language server for that