Currently the captioning code is a bit intertwined with the UI, and the
captioning is hard-coded towards microsoft speech API.
This patch abstracts captions to allow other APIs to be implemented
later.
Allows generating captions via the windows speech recognition API
(SAPI).
This is currently marked as experimental due to speech recognition
technology still being less than ideal. Speech recognition technology
in general is probably never going to be anywhere near perfect.
Microsoft's speech recognition in particular requires a bit of training
via the windows speech recognition tool to ensure it can dictate better.
Clear speech with a good mic is recognized fairly well, but casual
speech and/or speaking with a poor microphone will have some significant
issues. Captions can often be way off when speaking casually rather
than with clear diction.
