* Add PICO SDK
* Add RP2040 HAL implementation
* Add target Raspberry Pi Pico and its Upload method
* Modified PICO SDK-RTC because of conflict in name
* Use USB from boot, fix USB linking
* Try removing redundant init call
* Add SWD upload configuration, copy most init code from Pico SDK
* Fix RTC linking, fix ram size constant, fix test warning
* Add upload support for RPi Pico devices using Picotool
* Fix implementation of Tx IRQ for serial ports. BufferedSerial works now!
* Make PinNames.h pass pin validation
* Fix us ticker not working when debugging
* Fix us ticker double-init and manual fire interrupt function, us ticker tests now pass!
* Fix writing to rtc and rtc double-init, RTC tests now pass (except rtc-reset)
* Fix panic() not working from a critical section or ISR
* Fix compile failure due to extra LED1 definition
* Fix style
* Fix flash_api detection of invalid parameters, fix reset_reason to advertise the correct capabilities and implement them correctly
* Fix watchdog test warnings, fix broken hal_watchdog_get_reload_value(), fix missing frequency field in watchdog features
* Fix watchdog_reset failing to compile on some devices
* Fix us ticker fire_interrupt() not being callable from an ISR
* Fix incorrect license header
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Co-authored-by: Johnk1987 <odiin@seznam.cz>
Jamie Smith