Issue1395: Universal mode used to duplicate newlines when using read(1).

Issue1395: Universal mode used to duplicate newlines when using read(1).

"Universal newline" is now an incremental decoder wrapping the initial one,
with its own additional buffer (if '\r' is seen at the end of the input).

A decoder allows the tell() funtion to record the state of the translation.
This also simplifies the readline() process.

Now test_netrc passes on Windows, as well as many new tests in test_io.py