Implemented 'uniqueItems' keyword, and updated array generator to allow different types in the same array

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JSON LIBRARY UPDATES
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+List of changes:

	1) jsongen.erl:

		+Implemented keyword 'uniqueItems' for array types

		+Array generator updated: Now it generates values from different types in the same array instead of one (Unless 'uniqueItems' keyword is set as true)

		+Some cleaning up

	2) jsonschema.erl

		+Fixed a bug where the generator would crash when recieving an schema for 'additionalItems' keyword

	3) Added examples that test 'uniqueItems' keyword