Fasttracker II clone v1.67

• The song-to-WAV export screen now defaults to the tracker's bit depth and audio rate. This was actually the behavior for earlier versions of the FT2 clone, but I decided to change it back.
• The song-to-WAV exporter now allows rates up to 384kHz
• Alpha-based fade in for the about screen content (who cares..? :-)
• Some small text string changes (config and song-to-WAV export screen)
• Windows/macOS: Updated SDL to v2.26.5