[FEATURE] Allow specifying a pre-join callback to #dial

This is executed once prior to joining a call, and is passed the outbound call being joined.

#423
[FEATURE] Allow specifying rinback to `#dial` as a collection of audio
[FEATURE] Allow specifying ringback as a callback to start
[DOC] Fix changelog
[UPDATE] Depend on more recent Punchblock

Only just got output repeat support on Asterisk
Merge branch 'feature/dial_custom_ringback' into develop