`even?`, `odd?`, maybe others are underspec'd

[stanislowskij]

The current specs state that the argument should only be a number, not strictly an integer. This gives us a default error instead, which also has a misleading Babel message:

(s/fdef clojure.core/even?
  :args :babel.args/one-number)
(stest/instrument `clojure.core/even?)

after running (setup-exc):

babel.middleware=> (even? 1.2)

Expected an integer number, but a sequence 1.2 was given instead.

TODO: Find other cases