- also use queue.Queue instead of coros.Queue

- when notifying links, do not reschedule the rest of the links in case of
  an error; just print the traceback since that what the parent will do anyway

- now None (the default) means raise self, False means "silent" interrupt;
  True does not mean anything.

- add hex id in __repr__
- fix formatting bug in __repr__
- new __str__ that is split into several lines to make it more readable formatted that repr
- use __str__ when printng reports on exception raised by callbacks

although the feature is nice, it's did not work properly, e.g. for PriorityQueue.
neither the standard Queue nor coros.channel/queue do not support it and so are we now.

nicer error messages for asserts in wait_reader() and wait_writer()

greenlet.py: rearrange classes - put user visible stuff at the top and internal classes at the bottom

more responsive polling in kill[all](block=True); add join/joinall functions that just wait for a greenlet[s]

add test__queue.py: test for gevent.queue; based on the old tests for coros.Channel and coros.Queue plus a few new ones

Timeout: make __str__ return empty string, so that tracebacks are not cluttered with irrelevant information

greenlet.py: fix bug introduced in 117:ba38996ed7de: spawn_later ignored seconds parameter and launched everythin immediatelly