[ANN] ProblemSet.jl: create assignments for a class

An instructor frequently has to create sets of word problems for exams or home assignments. This entails two tasks: vary problems’ parts to make an assignment unique; and select a few problems from a larger set for assignment to an individual student. This package automates both tasks. I wrote it following the discussion of possible approaches; in the end, I decided to go with macro-based approach. The design of @model macro from the DynamicPPL package served as a base.

This relatively small package has already saved me quite a bit of repetitive work, so I am releasing it in the hope it will be useful to others. Criticisms and suggestions regarding the implementation and docs are welcome.