v5.0.0: add sx126x support, fix ESP32 integration

This is a major release, with potentially breaking changes.

Potentially breaking changes:

• all hal_... global symbols were renamed lmic_hal_.... The effect should be small for user code, but the compliance sketch needed to be fixed. So you may have problems.

Enhancements include:

• support for SX1261 and SX1262 radios
• documentation updates
• bug fixes

Caveats:

• I have not run the RedwoodComm LoRaWAN compliance tests for this release.
• I do not have a SX126x platform for test purposes (recommendations solicited)
• I have not investigated whether things can be integrated more cleanly with modern Arduino CLI/IDE. WIth Arduino CLI, you can pass #define from the command line; I imagine this is also possible with the IDE. There may be better ways to configure the library these days.

What's Changed (automatically generated)

• fix #840: enable device time request by default by @dhineshkumarmcci in #844
• add include for u1_t type by @supcik in #914
• Add driver for SX126x modems by @TristanWebber in #949
• This is version 4.2.0-pre2 by @terrillmoore in #964
• Fixed small typo by @Xraydylan in #956
• Initialize dht in ttn-abp-feather-us915-dht22 example by @jlesech in #902
• Update HOWTO-ADD-REGION.md by @wlwatkins in #879
• Address various issues related to SX126x support by @terrillmoore in #973
• Rename hal_ exports to lmic_hal_ by @terrillmoore in #974
• Fix #967: Add DISABLE_LMIC_FAILURE_TO on AVR test compiles to save space by @terrillmoore in #975
• Prepare documentation for v5.0.0 release by @terrillmoore in #980
• Release version v5.0.0 by @terrillmoore in #981

New Contributors

• @supcik made their first contribution in #914
• @TristanWebber made their first contribution in #949
• @Xraydylan made their first contribution in #956
• @jlesech made their first contribution in #902
• @wlwatkins made their first contribution in #879

Full Changelog: v4.1.1...v5.0.0