20200619

This is an experimental release.
If your VNA has a 2.8 or 3.2 inch display, use binary-ili9341.bin
If your VNA has a 4 inch display, use binary-st7796.bin

Changes since 20200525:

• Show whether device has FPU in dmesg
• UI performance improvements
• Larger font
• 4 inch display support
• Power off ADF4350 if the sweep range is < 140MHz
• AGC for lower noise floor below 1GHz
• Fix touchscreen calibration when flip display is enabled