Allow display synth to be used in conjunction with speech

[jteh]

Currently, the display synth is implemented as a synthDriver, so it cannot be used in conjunction with a real speech synthesiser. While the original intent was that this be used for sighted developers who would use it instead of a real synth, it may be useful for sighted teachers, trainers, etc. who want to follow what a screen reader user is hearing on screen. Therefore, it should be made possible for the display synth to be used in conjunction with a real synth.

Implementation Details

• The display synth could no longer be a synthDriver, as there can only be one synthDriver active at a time.
• It would probably have to be incorporated in functions of the speech module where speech is sent to the synth.
  • There are probably several cases where the synth functions are called directly. These calls should be abstracted to avoid code repetition.

[aleksey_s]

please, see my coment on #82.

[mdcurran]

Implemented in r3441.
Feedback welcome. The viewer itself has not changed, just the way its used internally in NVDA.
Rather than being a Display synth, you can now activate and deactivate the viewer from the Tools menu.
It now receives the text directly from the speech module, which means that it works independent of any speech synthesizer.