Fix underscore specs in seq and map destructuring contexts

Previously these wouldn't compile but now they do:

(defns abcde [[a string?] _ b string?] a)
(defns ghijk [{:keys [a string?]} _ b string?] a)

Generative testing now works for `defns`

Merge pull request #2 from alexandergunnarson/develop

0.2.0: Generative testing now works for `defns`

First working pass of `defns`; only known issue is in generative testing

Merge pull request #1 from alexandergunnarson/develop

0.1.0: First working pass of `defns`; only known issue is in generative testing