Add C-equivalent implementation of filter_english_letters.

Much like "filterWithoutEnglishLetters", it doesn't actually strip out
non-English characters. Instead, it's a filter that is used by
Latin1Prober to inaccurately remove HTML tags.  In reality, it removes
a lot of other stuff too, but I'm not sure if that was intentional yet.

Also cleaned up some of the pylint warnings for charsetprober.py.
Fix some pylint warnings in universaldetector.py
Made latin1 equivalent to windows-1252 when running unit tests.
A bunch of little clean up changes.

-  Made all classes use super() instead of explicitly listing calling
   parent __init__
-  Moved latin1 test file that's actually ascii into the correct dir
-  Removed some commented out lines of code that have been there forever
-  Made sure all attributes are defined in __init__ instead of at will
-  Other pylint warning fixes