Provide a way to modify metadata properties

[davidalk]

This proposal suggests a way we can modify a property that has metadata on it. Currently any properties that have metadata on them do not let you set that metadata using a set operator for example. The following proposed syntax would allow you to do that task:

func MyFunc:
	output:
		result string (1..1)
			[metadata scheme]
	set result:  "someValue"
	set result -> scheme: "someScheme"	

In addition to the above syntax we could also add a new with-meta operator which would allow you to make use of the constructor syntax when setting metadata. This would be especially useful when setting multiple metadata properties, see the following example:

func MyFunc:
	output:
		result string (1..1)
			[metadata scheme]
                        [metadata reference]
	set result:  "someValue" with-meta {
				  scheme: "someScheme",
                                  reference: "someReference"             
			    }