TODO

PoDoFo 0.5
    - Do not inherit from PdfTokenizer
    - Interactive forms support

PoDoFo 0.6:
    - convert PdfDocument / PdfStreamedDocument such that:
        + PdfDocument becomes PdfMemDocument
        + Common code moves to new shared base PdfDocument
        + PdfStreamedDocument does not depend on PdfMemDocument for base implementation
        + Most output-oriented tasks can be performed on any PdfDocument without caring
          what kind it is.
    - PdfString supports now unicode strings and conversions
        + PdfDocEncoding  to UTF16
        + UTF8 to UTF16
        + UTF16 to UTF8
    - Simple content stream parsing was added   
    - Support for reading & writing encrypted PDFs

FUTURE:
    - More filters (read & write)
    - Support for attaching an ICC profile to an image or content stream
    - Some more drawing routines (tiles, save and rstore?) also finish cleanup
      the existing ones revamp color support to be more general & support more
      types
    - PNG predictor functions in filters
    - CMYK image handling for podofoimgextract, images in different colour
      spaces in general.
    - Semi-streamed writing mode using normal in-memory document and a PdfStream
      class that can read input from a file / PdfInputStream on ::write() calls.
      (like PdfFileStream, but with support for user-supplied input files).
    - Streamline core datatypes to reduce repeated initialization, copy-construction,
      etc. Focus on limiting memory allocation/deallocation and heap fragmentation.
      Known trouble areas:
         + Small strings on heap in PdfString. Use an in-object buffer for
           small PdfStrings/PdfRefCountedBuffers since these are the most common type.