Add the following interfaces:

type Optioner interface {
  Option(*bson.Document)
}

Create specific Optioner types for Aggregate, Count, Delete, Distinct, Find, Insert, and Update.

For instance:

type AggregateOptioner interface {
  Optioner
  aggregateOption()
}

Reimplement the types in the option package to use this updated style and update the mongo package to use these as well.