1. Make sure Pico SDK libraries have the correct dependencies on other SDK libraries
2. Pico SDK libraries all have _headers variants to include the headers. This may facilitate building user STATIC libraries without
pulling in SDK code, though care will still need to be taken w.r.t. values of #defines
3. Make sure the _headers versions also have the correct dependencies
Note: There are a few exceptions to 1. for some non code libraries like pico_standard_link and pico_cxx_options
* Add pico_get_unique_board_id_string API
Add a new API to pico_unique which will turn the unique ID into a
canonical text string.
Use this API to update the USB device serial number in stdio_usb.
Supercedes #280
* Clean up -Wconversion=error issues
* Address review comments, fix api typing
Use cleaner binary-to-hex conversion. Update the length parameter to
use uint per the SDK standard .
- 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
