code clean-up and tweaks
tweaked reader.py
fixed a _TabularReader test
tweaked reader.py
DelimitedReader allows for escaped delimiters in input
DelimitedWriter can escape delimiters in output
modified tutorial.md
changed order of arguments to DelimitedReader and DelimitedWriter
added filter() method to FilteredIStream and FilteredOStream
renamed TextFilter to RegexFilter
added SliceFilter
pylint code tweaks
v0.2.1