Some function to generate v4 uuids
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Generate a random uuid:

	1> UUID = guid:v4().
	<<254,194,254,188,1,12,79,173,84,118,109,153,143,115,228,127>>

Convert to text representation:

	2> guid:unparse(UUID).       
 	"0ee31c01-26cc-43f1-a0f9-b52c6de7fcf7"

Check it's version:

	3> guid:version(UUID).
	4

Generate text representation drectly:

	4> guid:v4string().
	"68718f41-06ff-49a8-8283-00582b2d5269"