Fixed the silent-Synth bug.

Fixed a bug wherein the Synth class might be silent on 4-core
hyperthreaded or >4 core processors.
Added two new shortcuts (currently unconnected).
std::cout is now flushed before constructing SoundbenchMain to ensure
correct message printing order.
The RtAudio backend now uses the RtAudio class's functions to report
and deduce if the stream is running.
The RtAudio backend now spews warning.
Synth now inherits from a SynthBase parent class (to facilitate having
more fun later).
Added the Ctrl+I and Ctrl+E shortcuts.

For midi import and sound file export.
Fixed an unupdated tool tip.