Add ircv3.2 batch and batch channel and query buffer playback.

This adds [batch](http://ircv3.atheme.org/extensions/batch-3.2) support for client -> znc connections.  Also if the capability is enabled by a client, then channel and query buffer playbacks will be batched.

The batch `type` for this is `znc.in/playback`.  This is vendor-specific and follows the requirements defined [here](http://ircv3.atheme.org/specification/capability-negotiation-3.1)
The `reference-tag` is an MD5 of the channel or query name.
Additionally one parameter is provided, this is the name of the channel or query which is being batched.

At present I know of no clients which support batch, however @TingPing has indicated he is likely to add support to HexChat should this pull request be accepted.
Attila in `#ircv3` indicated that 3.2 was done.  I think we should be fine without prefixing.

Context:
```
13:15:44 <Attila> hi
13:15:48 <Attila> whats the status with the domain?
13:20:08 <SaberUK> Attila: whats his face pointed it to github
13:20:38 <Attila> o
13:20:43 <Attila> that means we can release 3.2
13:20:46 <Attila> if we had github pages
13:21:12 <Attila> i think we should make a gh-pages branch
13:21:24 <nw`> How close to 'done' is 3.2?
13:21:24 <Attila> and merge master when things move
13:21:32 <Attila> its done
```