LinkedQL: Match

[iddan]

Depends on #904 Define a Match step in LinkedQL that accepts a subgraph pattern and return entities matching the graph. Example:

Vertex().Match({ "http://example.org/likes": "http://example.org/bob" })

Will return all the entities which have a property pointing to Bob.

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This change is 

[iddan]

Quoting the Zen of Python:

"There should be one—and preferably only one—obvious way to do it."

Should we remove steps that can be replaced with .match()? Steps that can be easily replaced with .match():

• .Is()
• .Entity()
• .Entities()
• .Has()