v0.21

Release Notes:

• 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