fix pickle breakage with JSONDecodeError

pickle doesn't behave correctly with custom Exceptions, we workaround the issue
by explicitly defining how to pickle JSONDecodeError.
Merge pull request #78 from idank/master

fix pickle breakage with JSONDecodeError
update metadata for 3.3.1
Documentation fix for decoded string types
Merge pull request #82 from JuhaS/patch-1

Documentation fix for decoded string types