v4.1: Minor release: add battery status API, and fix bugs

See docs in README.md for release details.

Test Results

LoRaWAN 1.0.3 test results (prepared by RedwoodComm RWC5020B with software v1.321). (These will be updated as we have a chance to run the tests.)

• US915: EDT_US915_V103_ClassA_CERTIFICATION_USCA_TEST_RESULT.pdf. Passes all tests.
• AS923 (with settings for Japan, LBT and lower default dBi): EDT_AS923_V103_ClassA_LORAWAN_CERTIFICATION_AS_TEST_RESULT_NO_OptDR.pdf. Passes the required tests. The FSK downlink and SF7BW250 downlink tests do not pass, but these downlink speeds have not been not commonly used to date.

What's Changed

• Fix #763: use TimeLib.h in ttn-otaa-network-time example; this is v4.0.1-pre1 by @terrillmoore in #764
• Some more warning removed by @d-a-v in #791
• Update README.md by @PeeJay in #780
• Warning message for Adafruit Feather M0 pin mapping by @d-a-v in #755
• Support for TTGO-LoRa32-v2.1.6 by @ChrSchultz in #692
• MAX EIRP is 13dBm (= 19.95mW < 20mW) in as923jp by @ryos36 in #662
• Add control over battery level response for DevStatusAns MAC message by @terrillmoore in #799
• Fix #800: tweaks to compliance sketch by @terrillmoore in #801
• Fix #802: Prepare v4.1.0 release by @terrillmoore in #803

New Contributors

• @PeeJay made their first contribution in #780
• @ChrSchultz made their first contribution in #692
• @ryos36 made their first contribution in #662

Full Changelog: v4.0.0...v4.1.0