Enforce strict equality

[ricordisamoa]

As per #746 and for consistency with Python-based Jinja2, double equals should mean the same as the current triple equals, and triple equals should be dropped from syntax because there should be only one obvious way to do it.

	2.x	3.x
==	loose	strict
===	strict	not supported

[ArmorDarks]

I totally support it.

It's good practice not to use loose comparison in js community too, so I think it's double win

[carljm]

Yes, we should definitely do this for 3.0.