[FEATURE] Simple native->UniMRCP fallback in cases where native audio playback fails
[FEATURE] Support for multiple output documents on Asterisk native and UniMRCP fallback
[BUGFIX] Ensure that UniMRCP fallback uses only the broken doc
[FEATURE] Support multiple output documents on Asterisk (UniMRCP & Flite) and FS
[BUGFIX] UniMRCP doesn't support multiple documents
[BUGFIX] Output fallback should only execute <audio/> contents via MRCP

This does not yet take into account SSML docs with multiple <audio/> tags.
[BUGFIX] Ensure that TTS fallback docs inherit attributes of the original <speak/> element
[BUGFIX] Ensure that fallback ocurrs correctly with multipl audio tags
[CS] Split fallback node building out to a private method
[CS] DRY up output Playback options and early media
[CS] DRY up playback of files on Asterisk
[FEATURE] Fall back whole document if there are things other than audio at the top level
[BUGFIX] Ensure output really stops on a stop command
[BUG] Nokogiri is broken on JRuby (as always)
[BUGFIX] Properly skip native playback of TTS docs
[BUGFIX] Ensure prompt output is barged correctly on Asterisk ComposedPrompt
[BUGFIX] Fix Ast barge crash
[FEATURE] Allow playback of mixed TTS and audio docs
[BUGFIX] Fallback fix on JRuby
Merge branch 'release/2.1.1' into develop