Fix a few small issues, remove deprecated API

• Add a .join() method to wait for a timer that has been stopped to complete its final iteration. (Thanks, @pakal!)
• Remove ontimeout and params arguments (deprecated in 0.2)
• Properly pass args to RepeatingTimer
• Fix error if .stop() called before .start()

Fix deprecation issue, update API to match threading.Timer

• Replace time.clock() calls with time.perf_counter(), as time.clock is deprecated since python 3.3 and doesn't provide consistent behavior across different platforms.
• Replace ontimeout with function, and params with args and kwargs, to match the threading.Timer API.
  ontimeout and params are deprecated and will be removed in v0.3.
• Added lots of code comments to better explain how the module works.
• More detailed README