mapList: flatten function body
parse: allow startRule to be passed as string

default to 'SIP_message'
serializeable: cleanup transform option defaulting
parse: improve LWS folding
tests/rfc4475/dat/baddn.dat: append CRLF

Originally, there was no CRLF after the last message-header.
This caused the parse to fail for the wrong reason, so I've added it back in.
Note that the other bad*.dat do have the CRLF.
parse: move LWS folding to foldLWS method
parse: add line/column/input to error messages
Move generated parser customizations to own module.