Add PT_RUN_TASK() to regular Protothreads.
Remove NPT_SPAWN_SUCCESS() as it did not have an 
  overhead compared to NPT_SPAWN().
Optimize PT_YIELD() and NPT_YIELD().
Adapt SSD1306 driver to changes in xpcc::pt.

Protoface will now only have two methods:
- startTask() and
- runTask()

isTaskSuccessful() is deprecated.