TODO

This stuff would be great
- improved access to document level objects and data
  - bookmarks?
  - outline?
  - articles?
  - viewer prefs?
- Improve the speed of Encoding#to_utf8
- Tweak encoding mappings to differentiate between bytes that are invalid for an encoding, and bytes that are unchanged.
  poppler seems to do this in a quite reasonable way. Original Encoding -> Glyph Names -> Unicode. As of 0.6 we go straight
  from the Original encoding to Unicode.
- detect when a font's encoding is a CMap (generally used for pre-Unicode, multibyte asian encodings), and display a user friendly error
- Improve interpretation of non content stream data (ie metadata). recognise dates, etc



This might be useful, more research required
- Support for CJK text (convert to UTF-8 like all other encodings. See Section 5.9 of the PDF spec)
  - Will require significantly improved handling of CMaps, including creating a bunch of predefined ones

- Work out why specs/data/zlib*.pdf isn't parsed correctly when all the major PDF viewers can display it correctly

- Ship some extra receivers in the standard package, particuarly ones that are useful for running
  rspec over generated PDF files

- Add support for additional filters: CCITTFaxDecode, JBIG2Decode, DCTDecode, JPXDecode

- Add support for additional encodings:
  - Identity-V(I *think* this relates to vertical text. Not sure how we'd support it sensibly)

- Investigate how R->L text is handled

- fix all callbacks to only ever return basic ruby objects (strings, ints,
  attays, symbols, hashes, etc). No PDF::Reader::Reference or
  PDF::Reader::Font, etc.