Pre-release of V4 with proper channel hopping, bug fixes

[terrillmoore]

Documentation is lagging, but I've been using this and it seems to work. Key features:

• Added proper channel hopping using channel selection without replacement (rather than with replacement). This means that the sequence within a set of enabled channels should visit all the enabled channels (randomly) before re-visiting any in the set.
• Bug fixes for compliance testing.
• Various other features and contributions.

I've been testing this successfully with TTN V3. Not a lot of testing with non-US regions, although I've run some of the compliance tests.

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This discussion was created from the release Pre-release of V4 with proper channel hopping, bug fixes.