v4.0.0 release: assign channels without replacement (& other fixes)

[terrillmoore]

This is a major release, and (since it changes some of the contents of the LMIC structure, which are public) potentially breaking.

Potentially breaking changes include:

• Remove XCHANNEL support from US region Remove XCHANNEL support from US region #404
• Assign channels randomly without replacement US channel randomization not compatible with compliance test #515, Frequency selection is incremental upwards in MHz in cycles, not pseudo random as required by Lorawan Spec  #619, In function 'LMICeu868_nextTx': 'feasibleMap' may be used uninitialized #730.
• Don't allow LMIC_setupChannel() to change default channels Making arduino-lmic competible with arduino-esp32-2.0 #714
• Adopt semantic versions completely Add correct semantic version support #726.

Enhancements include:

• Add LMIC_queryNumDefaultChannels() Make value of NUM_DEFAULT_CHANNELS queryable. #700.
• Don't compile board config objects when we know for sure they'll not be used; compilers can't always tell Need #if in the code for the halconfig tables #736.

Important bug-fixes include:

• Don't accept out-of-range DRs from MAC downlink messages LMIC validDR() doesn't check out-of-range #723
• Implement JoinAccept CFList processing for US/AU US-like regions don't process JoinAccept CFList so don't adjust channel mask to match network #739.
• Correct JoinAccept CFList processing for AS923 CFList type 0 is not properly processed for regions with 2 default frequencies #740.

Fixes include:

• Fix some broken documentation references v3.3.0 README.md doc/README.md has outdated links #644, Fix #644: broken documentation references #646, Fix some links on README.md #673.
• Re-added CI testing, since Travis CI no longer works for us Migrate to new CI framework #647; fixed AVR compliance CI compile compliance sketch doesn't compile on AVR32, too big #679.
• Don't use defined() in macro definitions Code gives: warning: this use of "defined" may not be portable [-Wexpansion-to-defined] #606
• Fix a warning on AVR32 proposal : let the compiler optimize ? #709.
• Fix Helium link in examples Fix helium-otaa.ino link in examples #715, Fix helium-otaa.ino link in README again :) #718.

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This discussion was created from the release v4.0.0 release: assign channels without replacement (& other fixes).

[HeadBoffin]

Thanks for this, everyone's input on this project gives us great options for all sorts of devices, much appreciated.