XIAO RP2040, RP2040 SDK and APIs

A new release of Earle F. Philhower Arduino “core ” for RP2040 …

Release 2.4.0 - OTA support. I2S, UART, FreeRTOS, WiFi, IPv6 bug fixes

Add OTA.o to make p.io builds function (#755)
Add OTA update support (#711)
Increase FreeRTOS timer task stack to 1024 (#752)
Udp: default local_ip to IP_ANY_TYPE when IPv6 is enabled (#750)
IPv6 initial support from @oddstr13 (#748)
Fix typo in XIAO board name (#745)
Add board ElectronicCats Hunter Cat NFC (#741)
Fix UART wrong ::available() during wraparound (#739)
Stop random crashes while writing to flash (#730)
Increase LWIP MEM_SIZE to > TCP_SND_BUF (#731)
Adjust tcp_write size when memory is tight (#729)
Fix I2S timing (#728)
Add CMSIS defines to Platform.io (#721)
platform.txt: Add compiler flags for ARM CMSIS (#717)
Added to possibility to have extra compiler directives for a board. (#713)

Guglielmo