Decode format names and descriptions with ISO-8859-1.

Otherwise, we'll choke on the 'D\xe9j\xe0 vu' format.
Merge pull request #26 from weykent/decode-descriptions-as-latin1

Decode format names and descriptions with ISO-8859-1
Don't try to cast a python string to char *.

Doing this just results in an error, and isn't necessary anyway. cffi accepts
python strings as void * arguments.
Fix a bug; add a test for it.
Merge pull request #27 from weykent/remove-some-casting

Don't try to cast a python string in Image.from_buffer
Merge pull request #28 from weykent/fix-appending-to-images

Fix appending to images