Fix hyperlink syntax in the changelog

Commit 9578b3bd5ca introduced this error in the "check" target:

    warning: check: Duplicate explicit target name: "nir soffer".
Cleanup Darwin and FreeBSD compatibility code

get_peercred used duplicate code because different names were used for
the platform dependent constants. The constants were also using hard
coded values instead of values from the socket module when possible.

The platform is detected now using sys.platform, which is compile time
setting, and is easier to predict looking at Lib/plat-xxx directories in
the cpython source.

We use now the same names for both constants, and the value defined in
the socket module if the name is defined, or the hardcoded value. The
new private constants are moved near the function using them.
Add a known issues section for #8.
Add a `daemon_connection` install option.
Move the subprocess code in a helper file. Fixes #15.
Add tests for daemon_connection.
Oooops, fix "huge typo". Tests weren't testing correctly.
Skip the daemon tests on eventlet. Convert other conditional tests to use the skipif marker.
Fix the condition on the test_signalfd_weirdness_negative skip.