Fix names of some history variables

The history lists ack-regexp-history ack-literal-history (used in
`ack-and-a-half-read') don't actually exist. Their names are actually
ack-and-a-half-regexp-history and ack-and-a-half-literal-history. Fix
this typo.
Add `ack-and-a-half-with-args' for running ack with arguments

Sometimes it's useful to be able to pass extra arguments to
`ack' (e.g. "--ignore-dir=foo"). Add a function to allow this.