* 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
- Add recursive_mutex
- Make all locking primitives and sleep use common overridable wait/notify support to allow RTOS
implementations to replace WFE/SEV with something more appropriate
- Add busy_wait_ms
In C, func() is a function taking an unspecified number of arguments,
vs func(void) a function taking no arguments. In C++ both forms indicate
"no arguments."
Update these headers to use the (void) form, which is correct in both
languages and avoids complaints when -Wstrict-prototypes is specified.
