Update to v0.31

Makefile

@@ -1,6 +1,6 @@
 
 export FW_MAJOR := 0
-export FW_MINOR := 30
+export FW_MINOR := 31
 
 TARGETS := all blinky clean dist windist mrproper f1_ocd ocd flash start serial pysetup
 .PHONY: $(TARGETS)

RELEASE_NOTES

@@ -3,6 +3,10 @@
 ** Keir Fraser <keir.xen@gmail.com>
 ************************************
 
+** v0.31 - 8 October 2021
+ - F1: Support Low-Density STM32F103C6 chips, 32k Flash, 10k SRAM
+ - V4: Increase USB buffer size from 16kB to 64kB
+
 ** v0.30 - 12 August 2021
  - New board type: V4 Slim (AT32F403 MCU, laptop drive interface)
  - F7 Slim: Support Disk Change Detect (used by WinUAE floppy bridge)