Add initial implementation of an ASCIIHexFilter.
Add initial work on Reader and Writer implementations of ASCIIHexDecode and FlateDecode encoder/decoder pairs.
Add additional work on development of FlateDecode, LZW, and ASCIIHexDecode Filters.
Use the zlib encoder to generate a stream that can be decoded with "FlateDecode".
Clean up stream filter test cases.
Add StreamFactory, StreamFilterFactory, and PageFactory.
Add Append() method to pdf.Array.
Don't modify dictionary in pdf.Stream.Serialize() and preserve any filter specs required to read a pre-existing stream.
New filters are appended to the old filters so that new filters can be
applied even if the reader is missing an implementation  for a
pre-existing filter.
Add preliminary code for reading pre-existing streams with filters.
Add test for reader for streams with filters.