$top and $skip with expressions

[HeikoTheissen]

Allow $top and $skip with "collection expressions" defined like here:

odata-abnf/abnf/odata-aggregation-abnf.txt

Lines 188 to 189 in c700211

	; Expressions evaluable on a collection
	collectionExpr = commonExpr ; but where every firstMemberExpr must be a currCollectionExpr

Employees?$top=Age

would not be allowed, because Age cannot be evaluated on a collection of Employees. But

Managers?$expand=Employees($top=$it/Age)

would be allowed, since $it/Age is the age of one instance of Managers.