Add papers describing PID controller implementation for self-regulating systems

docs/CHANGES.md

@@ -1,11 +1,14 @@
 ## Changelog
 
 ### v0.75-alpha2
-- Use internal oscillator without CKDIV8.
 - Increase available memory to 4096 bytes.
+- Use external 18.432 MHz crystal oscillator.
+- Consolidate unfinished tasks and update documentation.
+- Add papers describing PID controller implementation.
+- Move fuse Makefile variables to general settings.
 - Change ARCH and MCU settings to match chip signature.
 - Update module 'pwm' to run on atmega1284p hardware.
-- Update module 'usart' to run on atmega1284p hardware.
+- Update module 'uart' to run on atmega1284p hardware.
 - Update module 'watchdog' to run on atmega1284p hardware.
 - Update module 'memory' to run on atmega1284p hardware.
 - Update Makefile settings for new chip architecture.