Handle transfer-encoding:chunked; misc. replay bugs.

- Add a ChunkedLineReader to deal with replays with the
transfer-encoding: chunked header.
- Catch UnicodeDecodeErrors caused by multibyte characters getting
split during buffering.
- A couple of tiny bugs in replay.py
Merge pull request #2 from jcushman/master

Handle transfer-encoding:chunked; misc. replay bugs.