Expand support of TYPE extraction for literals and predicates too, in addition to nodes about badwolf HOT 2 OPEN

Thanks for putting this explanation together @rogerlucena. I was wondering if you have settled on using = vs the is,covariant, contravariant combo alternatives for the comparison primitives.

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Following Xavier's comment, an alternative to using = is implementing a is keyword to be used when comparing types. For example:

HAVING ?o_type is ^^type:predicate:immutable;

In the case of TYPE bindings for nodes, it would also be possible to implement the covariant and contravariant keywords to unlock the use of the hierarchies that are intrinsic of node types (such as /country/corp and /country/corp/employee). This could be helpful for allowing more ellaborate comparisons inside HAVING clauses, an alternative for what was requested with #122.

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