Exptest

This is a test from [Regular Expression Matching Can Be Simple And Fast ](http://swtch.com/~rsc/regexp/regexp1.html). A lot of regexp implementations in different languages fail this test.

Here’s the evidence that regexp-applicative passes the test. Tested with v0.1.3

import Text.Regex.Applicative
import Data.Traversable

rep n r = sequenceA $ replicate n r

r n = (,) <$> rep n (sym 'a' <|> pure 'b') <*> rep n (sym 'a')

<!-- A hack to separate two blocks :( -→

*Main> replicate 30 'a' =~ r 30
Just ("bbbbbbbbbbbbbbbbbbbbbbbbbbbbbb","aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
(0.08 secs, 8400496 bytes)