pep8, typos and cleanups
simple fixes from pylint
extract some code in _parse_args__pattern to
_parse_args__split_bracketed_pattern
renamed variables
readability
small editorials
params from argparse have higher priority then from -s
editorials
work only with absolute paths
subst now better fights with non-ascii data
alias --pattern-and-replace to -s (was only --pattern_and_replace)