* add stdio_usb_connected() method
* add PICO_STDIO_USB_CONNECT_WAIT_TIMEOUT_MS to allow waiting for CDC connection during init(*
* add puts_raw and putchar_raw to skip any CR/LF translation
* pico_stdio_usb: be more explicit about includes, fix warning (#257)
* pico_base: NDEBUG backwards for absolute_time_t (#255)
* pico_util: missing extern C in queue.h (#249)
* build: remove -march which was masking -mcpu, now SVC available (#253)
- setting baud rate to magic value (default=1200) will cause a reset to BOOTSEL mode
- a VENDOR interface along side the CDC interface can be used to reset via refular flash boot, or into
BOOTSEL mode with control for the reset_usb_boot parameters for the latter
either method can be configured/enabled/disabled via #define
