Make the example error free

Without padding b"my secret message" is not divisible by AES's
block size and thus would throw an error.
Merge pull request #40 from dstufft/fix-docs

Make the example error free
Fix the packaging meta-data
Include all of our files in the distributions, and install packages
Ignore the dist directory
Merge pull request #41 from dstufft/fix-setup

Fix setup