Metamagic-json

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Changes:

* Fix a memory leak in the C implementation of mapping encoder.

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Changes:

* We do not escape '/' characters now (Python standard library
'json' module does not either)

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Changes:

* Python encoder casts to int & float explicitly before serialization
(to follow C encoder logic more closely)

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Changes:

* Add json.loads and json.loadb methods

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Fixes:

* Fix encoding of aware datetime and time objects when UTC offset is negative

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Changes:

* Always encode '<', '>' and '&' as Unicode sequences