Add support for wrap_func

[flaper87]

If we run out of attempts, it'd be nice to have a final chance to inspect the result of the call before the final reraise or return are done. I think this could be done by having a wrap_func called passing in the attempt

[gulducat]

Just in case someone stumbles across this (like I did), I made a change to tenacity (after seeing #65) that covers this.

from tenacity import retry, stop_after_attempt

def inspect_last_attempt(last_attempt):
    print(dir(last_attempt))
    # do whatever you might like to do here

@retry(stop=stop_after_attempt(3), retry_error_callback=inspect_last_attempt)
def aw_shucks():
    raise Exception('aw dang')