Issue 24878: Add docstrings to selected named tuples

Add docstrings to some named tuples that could benefit from it (there was more documentation or useful information other than just the field name).  This makes the help() on those named tuples much more informative.

For example:

>>> import sched
>>> help(sched.Event)

class Event(Event)
 |  Event(time, priority, action, argument, kwargs)
 | 
...
 |  ----------------------------------------------------------------------
 |  Data descriptors inherited from Event:
 |  
 |  action
 |      Executing the event means executing
 |      action(*argument, **kwargs)
 |  
 |  argument
 |      argument is a sequence holding the positional
 |      arguments for the action.
 |  
 |  kwargs
 |      kwargs is a dictionary holding the keyword
 |      arguments for the action.
 |  
 |  priority
 |      Events scheduled for the same time will be executed
 |      in the order of their priority.
 |  
 |  time
 |      Numeric type compatible with the return value of the
 |      timefunc function passed to the constructor.

New changeset 40f2bbb922e6 by Raymond Hettinger in branch 'default':
Issue #24878:  Add docstrings to selected namedtuples
https://hg.python.org/cpython/rev/40f2bbb922e6

I see some typos in aifc.py:
+_aifc_params.sampwidth.__doc__ = 'Ample width in bytes'
+_aifc_params.compname.__doc__ = ("""A human-readable version ofcompression type

Should that be "Sample width" and "of compression"?

New changeset 4432c441b639 by Raymond Hettinger in branch 'default':
Issue #24878: Fix typos and line wrap
https://hg.python.org/cpython/rev/4432c441b639

Thanks Petr