Add missing #argument fluent method to ConstructMatcher.

Fix assorted documentation issues.

Current spec status:
  1.9.3: 200 examples, 0 failures in 0.16547 seconds.
  2.0.0: 215 examples, 0 failures in 0.07833 seconds.
  2.1.2: 238 examples, 0 failures in 0.13244 seconds.