Automatically reply to heartbeat requests (ping) unless given "?pong=0"

[clue]

Quassel uses "heartbeat" messages as a keep-alive mechanism to check the
connection between Quassel core and Quassel client is still active. This project
will automatically respond to each incoming "ping" (heartbeat request) with an
appropriate "pong" (heartbeat response) message. If you do not want this and
want to handle incoming heartbeat request messages yourself, you may pass the
optional ?pong=0 parameter like this:

$factory->createClient('quassel://localhost?pong=0');

This is technically a BC break because consumers of this package would need to handle this manually previously and switching to this new behavior means that this consumer code may now send duplicate heartbeat replies. In practical terms, adjusting this is rather straight-forward and this makes consuming this library easier for most common use cases.

Builds on top of #36 and its much improved test suite