constructing lru_cache (C implementation).

* Fix ResourceWarning warnings in test_streams
* Return True from StreamReader.eof_received() to fix
  http://bugs.python.org/issue24539 (but still needs a unittest).
  Add StreamReader.__repr__() for easy debugging.
* remove unused imports
* Issue #234: Drop JoinableQueue on Python 3.5+

Move compatibility helpers for the different Python versions to a new
asyncio.compat module.

If exc_traceback is None we shouldn't print a traceback header
like described in the documentation.

The fix for Issue #21217 introduced a regression that caused
`inspect.getsource` to return incorrect results on nested
functions.  The root cause of the regression was due to
switching the implementation to analyze the underlying
bytecode instead of the source code.

This commit switches things back to analyzing the source code
in a more complete way.  The original bug and the regression
are both fixed by the new source code analysis.

This commit simplifies async/await tokenization in tokenizer.c,
tokenize.py & lib2to3/tokenize.py.  Previous solution was to keep
a stack of async-def & def blocks, whereas the new approach is just
to remember position of the outermost async-def block.

This change won't bring any parsing performance improvements, but
it makes the code much easier to read and validate.

* Tests that index.html is served, rather than an automatic directory listing
* Tests that there is no extra data sent after the response

Patch by Martin Panter.

This commit fixes how one-line async-defs and defs are tracked
by tokenizer.  It allows to correctly parse invalid code such
as:

>>> async def f():
...     def g(): pass
...     async = 10

and valid code such as:

>>> async def f():
...     async def g(): pass
...     await z

As a consequence, is is now possible to have one-line
'async def foo(): await ..' functions:

>>> async def foo(): return await bar()

Patch by Jacek Kołodziej.

Patch by Jacek Kołodziej.

Patch by Kai Groner.

According to the documentation, they must be decorated as classmethods.