* cows/default.cow: Removed to avoid conflicts with cowsay;
python.cow is now the default cow.
* cows/python.cow: Slightly improved.
* scripts/pysay: General refactoring.
Removed unused imports.
Fixed quotation marks inconsistency, now use single quotes only.
Added docstrings.
The code is now PEP8 compliant.
(get_cow_path): Use 'cow' instead of 'f'.
* scripts/pysay (main): The argument parser has its own class now.
(PysayParser): New class.
* scripts/pysay (cow_parse): Corrected gotcha in the substitutions
within perl_cow.
(fill): Corrected gotcha in the regex of 'paragraphs'.
(construct_balloon): Corrected gotcha in the 'formatstr' expression.
* scripts/pysay (construct_face): Fixed bugs: use unicode and
consider only the first two characters for 'eyes' and 'tongue'
passed with the -e and -T arguments.