Beat Looper：Become beat machine master right now

Aug 9, 2018

1. Add "Section" settings for modifying section count and beat type;
2. Add "Pitch" controller for adjusting the pitch value of instruments;
3. Buid in user instructions manual;
4. Add new feature that you can change the volume and timbre by long press and press one instrument;
5. Optimize some user interface for making app more friendly;
6. Fix some crash bugs.