Log Message:
py-pdfrw: update to 0.4

pdfrw 0.4:

Fixes, enhancements, and new examples:
- Python 3.6 added to test matrix
- Proper unicode support for text strings in PDFs added
- buildxobj fixes allow better support creating form XObjects
  out of compressed pages in some cases
- Compression fixes for Python 3+
- New subset_booklets.py example
- Bug with non-compressed indices into compressed object streams fixed
- Bug with distinguishing compressed object stream first objects fixed
- Better error reporting added for some invalid PDFs (e.g. when reading
  past the end of file)
- Better scrubbing of old bookmark information when writing PDFs, to
  remove dangling references
- Refactoring of pdfwriter, including updating API, to allow future
  enhancements for things like incremental writing
- Minor tokenizer speedup
- Some flate decompressor bugs fixed
- Compression and decompression tests added
- Tests for new unicode handling added