Make _NoopLog better match a file-like object in case its used as wsgi.error. Doc cleanups in pywsgi.

Quiet lookup errors from the threadpool by default. Ref #617 that was also mentioned in a private email.

This masks an underlying PyPy bug referenced in the changelog, so it's still not as efficient as it
could be, but it's the best we can do on currently released PyPy.

Impact for CPython2 appears negligible (and none at all for CPython 3, since we don't support PyPy3).

Stop installing cffi on RTD. The compilation error *with* it is worse than the import error *without it*. (Compilation error is because only on PyPy do we move libev.h into the right place) [skip ci]

Actually make 'greenlet' a link. Fixes #386. Staged at http://python-gevent.readthedocs.org [skip ci]

Document the library updates, and call special attention to the changes in the c-ares configure script that can break on some CFLAGS/LDFLAGS configurations. [skip ci]

Add missing readable/writable methods to FileObjectPosix. Fixes at least help() on a monkey-patched Python 3

Updates for gevent.os.fork/waitpid, mostly documentation, but also make it possible to switch off the waitpid behaviour and access the 'basic' fork function.

- De-dup wait_read, etc, from socket2 and socket3 and call them out as gevent extensions.
- Doc create_connection on socket2 and socket3 since its a standard interface.
- Docstrings for gethostbyname, etc.

Debugging code for RTD and util/cythonpp.py. Also, don't force /usr/bin/python, use the environment python (better for virtual envs). [skip ci]