minor correctness fix
Fix thread priority when building in release mode.

The call to set prority was wrapped in an assert() so it was
removed when building in release. this is fixed now.
Module renaming (commit 1).

Module has been renamed to LedBuzzer as it handles some buzzer
the same way it handle LED.

This is true for most buzzer than can be turned on or off and
do not require toggling them at a given frequency: most card
reader should behave like this.
Renamed module (commit 2).

Add a FBuzzer class that is simply an alias to FLED since both
object offer the exact same behavior right now.