Datacrunch

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* Add contract and pricing parameters in datacrunch.instances.create()

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* Fix volume.increase_size()
* Fix volumes.get()

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* Added spot price to instance types

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* Added locations endpoint and location code parameter to the availability endpoints

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* Added location constants
* Refactored the code to send `location_code` instead of `location` when creating an instance or a volume

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* Fixed a bug where token refresh failed