watcher:  restart after command only if running

After processing a command from the client, only restart the watcher if
the watcher was already running.  This allows the client to first set
options on the watcher before starting it.
Merge pull request #654 from jsbronder/restart

watcher:  restart after command only if running
Add helper methods to CircusPlugin for parsing the received data

Before this change, each plug-in had to split data into "topic, msg", the u(topic).split('.'), then implicitly know that topic_parts[1] was the watcher name and topic_parts[2] was the action. Also, if the plug-in wanted to parse the msg portion, it needed to import zmq.utils.jsonapi. Not at all obvious to a plug-in writer.
Change buffering in docs to 1 since 0 doesn't work for text files on Py3
Fix line length for flake8
Merge pull request #657 from scottkmaxwell/parsing-helpers-for-plugins

Parsing helpers for plugins
Correct a typo in hooks' documentation
Merge pull request #659 from Khady/patch-1

Correct a typo in hooks' documentation