Firmware support fixes
This version primarily implements a new hardware abstraction layer, which allows the software to identify the correct commands to use for scanning with the various firmware versions.
It also includes a new "About" window, which shows the NanoVNA firmware version, if available.
Also included is a new function to automatically check if there are new versions of NanoVNA-Saver available, either on program start, or from a button in the About window.
Other changes:
- Additional colour for secondary reference traces, for the R+jX chart
- A first version of a bandstop filter analysis function
- Updated octave/decade roll-off for filters to show the roll-off between -10dB and -20dB
- New load/save boxes for S1P and S2P files, which should now automatically set the extension for these files.
I look forward to hearing your feedback!