sigonasr2, Sig, Sigo

Results 2 issues of sigonasr2, Sig, Sigo

Functions added: `void WaveEngine::PauseWaveform(const PlayingWave& w)` `void WaveEngine::ResumeWaveform(const PlayingWave& w)` `void WaveEngine::RewindWaveform(const PlayingWave& w)` Useful features that are beneficial to the header.

To compile with emscripten, use `-s USE_SDL_MIXER=2` for the setting flags. #11