def count(limit = false)
      command = { count: collection.name, query: selector }
      command.merge!(skip: operation.skip, limit: operation.limit) if limit
      result = collection.database.command(command)
      result["n"].to_i
    end
def count(limit = false)
      command = { count: collection.name, query: selector }
      command.merge!(skip: operation.skip, limit: operation.limit) if limit
      result = collection.database.command(command)
      result["n"].to_i
    end
Get the count of matching documents in the query.

 @example Get the count.
   db[:people].find.count

 @return [ Integer ] The number of documents that match the selector.

 @since 1.0.0