Generate patches for native type schema deficiencies

[alexzielenski]

Adds some code to the native schema downloader that also generates patches to workaround known deficiencies in native schema.

Fixes #60

Currently included patches:

1. Allow empty byte format strings
2. Allow empty date-time format strings
3. Remove default: {} where it does not make sense

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[richardvflux]

I just built the docker image for this two hours ago and now hit this bug and notice you fixed it an hour ago 😂 Nice work!

[eddycharly]

Awesome !