This adds an excmd interface to the Web Speech API (TTS), which allows
users to read text out and set voice and parameters via config options.
Excmds:
- ttsread: reads out the given text or element content (CSS selected)
- ttsvoices: lists available voice names (can be used in the
'ttsvoice' option)
- ttscontrol: stops the current reading (should also pause/resume,
but that doesn't seem to work right now)
Config options:
- ttsvoice: the name of the voice to use
- ttsrate: (0.1-10)
- ttsvolume: (0-1)
- ttspitch: (0-2)
Also the ;r hint submode is added which reads the textcontent of the
element with the configured voice
