move formatter to own sub package
change Formater interface for convenience

Format() now writes to an io.Writer instead of returning an io.Reader
rename type ProcessEvent -> EventProcessorFn
shorten variable names in examples
'make test' should run all tests
'make integration' should be self-contained, e.g. fetch dependencies, clean up and test
fix parsing of PyStrings, do not include line breaks in lines
adapt formatter changes