Add per-channel Swing configuration (#7)

Select swing amount from a percentage range of the beat starting a 50% (unchanged) to a max swing amount of 95% (about 1/32nd note before end of period). Swing percentage shows an indicator marker when the percentage lines up with a quantized note on the grid.

This is probably going to be the last feature because it is pushing up against the limits of available dynamic memory.

Out of scope changes:
- selecting parameters / values no longer wraps
- reduce dynamic memory used in processClockTick
- various readability formatting

Reviewed-on: https://git.pinkduck.xyz/adam/libGravity/pulls/7
Co-authored-by: Adam Wonak <adam.wonak@gmail.com>
Co-committed-by: Adam Wonak <adam.wonak@gmail.com>

examples/Gravity/save_state.h

@@ -9,7 +9,7 @@ struct AppState;
 
 // Define the constants for the current firmware.
 const char SKETCH_NAME[] = "Gravity";
-const byte SKETCH_VERSION = 3;
+const byte SKETCH_VERSION = 4;
 
 // Define the minimum amount of time between EEPROM writes.
 static const unsigned long SAVE_DELAY_MS = 2000;
@@ -41,6 +41,7 @@ class StateManager {
         byte base_probability;
         byte base_duty_cycle;
         byte base_offset;
+        byte base_shuffle;
         byte cv_source;       // Cast the CvSource enum to a byte for storage
         byte cv_destination;  // Cast the CvDestination enum as a byte for storage
     };