Update to v0.21

Makefile

@@ -1,6 +1,6 @@
 
 export FW_MAJOR := 0
-export FW_MINOR := 20
+export FW_MINOR := 21
 
 TARGETS := all blinky clean dist windist mrproper ocd flash start serial
 .PHONY: $(TARGETS)

RELEASE_NOTES

@@ -3,6 +3,16 @@
 ** Keir Fraser <keir.xen@gmail.com>
 ************************************
 
+** v0.21 - 10 September 2020
+ - Support new Greaseweazle model: F7 Lightning Plus
+ - Fixes for older drives
+   - 50us index mask, avoid double triggering on the index signal
+   - Increase default head-step delay to 5ms
+ - Windows: Install the CAPS/SPS IPF library automatically
+ - New command 'gw seek' to seek to specified drive cylinder
+ - New syntax for specifying Greaseweazle device name on command line
+   - eg 'gw read --device COM3 a.scp'
+
 ** v0.20 - 1 July 2020
  - gw write: New options --erase-empty and --double-step
  - gw update: Fix COM redetect on Windows running Bitdefender