First pass at playing with explicit properties
More properties notes
Docstring typo
Add frequency generator combinator
Wrap generators in [:gen ...] tuple

This is so we can identify them. Just using `ifn?` isn't good enough,
since many things our tests will return will be functions. We need a
good way of distinguishing them, so the sake of writing nested
properties.
Tests passing with reified properties
Fix `return` generator
Note and remove unneeded argument
Merge branch 'feature/explicit-properties'