pdf-merge.py: Bump to version 0.3

Changes since 0.2:

77a9ba6 pdf-merge.py: Upgrade to Python 3.x
0c3b4c3 pdf-merge.py: Add KEYWORD metavar for --keyword.
8003741 pdf-merge.py: Add -v/--version option
8966242 pdf-merge.py: Fix 'perserving' -> 'preserving' typo in module doctest
5cef5f7 pdfmerge.py: Bump copyright year
71c7be5 pdf-merge.py: Update dump parser for pdftk v1.45
c75bc05 Add `--pdfmarks` option to pdf-merge.py.
abdbff4 Remove `[:-len('�')]` from Unicode parsing of pdftk output in pdf-merge.py.
8efa8f6 Credit Larry Cai <larry.caiyu@gmail.com> for suggesting Unicode handling.