v0.4

Preliminary support for programmatic access to error details (Issue #5). There are certainly some corner cases that don't do the right thing yet, but this works mostly.
In order to make this happen (and also to clean things up a bit), a number of deprecations are necessary:
- stop_on_error is deprecated in Validator.__init__. Use Validator.iter_errors() instead.
- number_types and string_types are deprecated there as well. Use types={"number" : ..., "string" : ...} instead.
- meta_validate is also deprecated, and instead is now accepted as an argument to validate, iter_errors and is_valid.
A bugfix or two

v0.3

Default for unknown types and properties is now to not error (consistent with the schema).
Python 3 support
Removed dependency on SecureTypes now that the hash bug has been resolved.
"Numerous bug fixes" -- most notably, a divisibleBy error for floats and a bunch of missing typechecks for irrelevant properties.