Add pcre language. #118

Turns out grep based hooks are a little more complicated than I initially thought in #21

There's a false positive in the following case with xargs:

batch1: no matches returns 1
batch2: matches returns 0

xargs will report this and this the same:

batch1: no matches returns 1
batch2: no matches returns 1

The first one should fail, the second one should succeed.