[voiceinteraction] VoiceXML platform builtins

During our last call we talked about generic capabilities that could be
included in any Intelligent Personal Assistant platform, and it seemed like
we could get some ideas from VoiceXML (https://www.w3.org/TR/voicexml20/)
built in events. 

I took an action to look them up. 

They are:

Help

Nomatch

Noinput

Error

 

These could be used in any VoiceXML document and a VoiceXML-compliant
platform would be required to provide some kind of handler, that is, not
crash or hang, if they occurred. It was considered to be poor design on the
developer's part to let the platform default handler actually handle these
events (by not providing overrides), but they had to be there. 

In our architecture, the analogy could be that these capabilities are always
part of the IPA Service.