minor tweaks and code clean-up
refactored _Reader and _Writer
added filter.py module
code clean-up
added example to tutorial.md
added buffer.py module
refactored _ReaderBuffer.next()
added section on buffers to tutorial.md
added _WriterBuffer to buffer.py module
minor tweaks and clean-up
refactored date formatting
code clean-up
modified tutorial.md
v0.1.4