Hypothesis-jsonschema

- Improved handling of the `contains` keyword for arrays

- Improved canonicalisation and merging for a wide range of schemas,
which as usual unlocks significant optimisations and performance
improvements for cases where they apply.

- Future-proofed canonicalisation of `type` key.

- Better internal canonicalization, which makes current and future
optimisations more widely applicable.
- Yet another fix, this time for negative zero and numeric bouds as floats
with sub-integer precision. IEEE 754 is *tricky*, even with Hypothesis!
- Fixes handling of `enum` with elements disallowed by base schema,
handling of `if-then-else` with a base schema, and handling of regex
patterns that are invalid in Python.

- Fix the fix for numeric schemas with `multipleOf` and exclusive bounds.

- Supports merging schemas for overlapping `patternProperties`,
a significant performance improvement in most cases.
- If the `"type"` key is missing, it is now inferred from other keys
rather than always defaulting to `"object"`.
- Fixed handling of complicated numeric bounds.