use CREATE_WOUT_YIELD on uart0 thread creation

This should remove a race condition in the case that some uart event
occurs after the uart0 thread has started and before control has
returned to the calling thread, as uart0_handler_pid would not have
been set yet.
break long line
Merge pull request #257 from LudwigOrtmann/uart0_thread_create

use CREATE_WOUT_YIELD on uart0 thread creation