Parametric nesting house for orchard mason bees

A parametric module to generate a hexagonal nesting house for
[Orchard Mason Bees](http://en.wikipedia.org/wiki/Orchard_mason_bee).

This prints in 3 parts so that it can be broken down for storage, and for easy access to the nest holes for cleaning. Being able to disconnect the nest from the base also allows it to be easily moved to different pollination zones or under cover for winter storage. Along with the shroud, the slight downward tilt of the nest is intended to keep the nest pro