Get should not fail with InvalidArgumentException when projecting on more than 16 fields

Imposing a limit of 16 is not consistent with the RFC:

A new feature of Get is to allow "projections" of document fragments for a given path. Based on Sub-Doc API, the maximum number of fields that can be projected is 16. Once the 16 field limit is reached, the entire document will be fetched using the standard Get command.

This should be an easy fix (just removing the check for the number of projections). C++ already has the functionality to fall back to the full document fetch.