added protocol analyzer for USB

[StuckNomad]

• Added Protocol Analyzer for USB 2.0.
• Supports both Low-Speed and Full-Speed.

Mode	Preferred Sampling rate
Low Speed	15Mhz
High Speed	100Mhz

Mode	Preferred triggers
Low Speed	Positive edge trigger for D+ channel
High Speed	Positive edge trigger for D- channel

[mengstr]

Out of curiosity - why is the recommended sample rate 100MS/s for the Full Speed? It is not evenly divisible by the bit rate. The only thing I can think of is the granularity of the available sample rates, so I guess that's it?

[StuckNomad]

My initial plan was to calculate bits per sample by dividing the sampling rate by bit rate. But the D+ and D- channels were often misaligned and caused issues in determining J and K states. I implemented a workaround for this and even divisibility is not required anymore. Moreover, I've observed that this misalignment goes away at higher sampling rates, which is why I chose 100Mhz instead of 96Mhz.

[gusmanb]

Thanks for the analyzer and your participation. I will test it this weekend and if it works I will accept the PR.

Thank you!