Generated structs should have the omitempty tag option

[andreykaipov]

Would avoid situations like this described in #5 (comment)

[andreykaipov]

Every field now has omitempty by default except any boolean field, which all omit omitempty.

For example, in the case of SetSceneItemProperties, the Visible field can't have omitempty because making it invisible would involve setting it to false, at which point the JSON encoder will omit it from the sent request.

I imagine there's a few integer fields whose empty value (0) happens to be a valid value in a request, so in the future more fields may omit omitempty, but that's something to worry about later ... 😄