Document all ncap2 functions in User Guide

[czender]

A user recently requested directions to functionality implemented by make_bounds() and was unaware of its existence because it is undocumented. This reminded me that many ncap2 functions listed by ncap2 -f (which few people know exists) may be undocumented. This task is to create a list of the undocumented functions, paste it here, and then to add a description of each to the User Guide before closing this issue. Features worth implementing are worth documenting.