Replace [4]float return value from Extenter.Extent() w/ Extent struct.

[JivanAmara]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 52

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-2.3%) to 77.503%

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Files with Coverage Reduction	New Missed Lines	%
bbox.go	3	94.47%

Totals
Change from base Build 50:	-2.3%
Covered Lines:	2353
Relevant Lines:	3036

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💛 - Coveralls

[gdey]

What is the reasoning behind this change?

[gdey]

@ARolek let me know that we discussed it and decided this is the direction we should move. Found the discussion, but you guys did not specify the reasoning:

jivan [4:31 PM]
I think we should standardize the extent parameter type. Any preference for explicit [4]float64 vs geom.Extent?
Or just use the Extenter interface for parameters?

arolek [4:50 PM]
geom.Extent

I'm fine with the direction; the reason I had it as [4]float64 was to make it easier for other to implement the Extender interface. I can see the reasoning for geom.Extent as well though, and since they are aliases it should not be a big deal to go back and forth. So, my reasoning was that if you need the extra methods you could do:

    ext := geom.Extent(obj.Extent())

That would still allow other to implement Extent without knowing about geom.
There is a wart in the above, which is to pass ext as an Extenter you would have to pass &ext as the geom.

[ARolek]

Sorry, @JivanAmara this was a misdirection on my part. We should standardize around [4]float64.

[JivanAmara]

@gdey, @ARolek
So Extent() & BufferedExtent() should return [4]float64?
https://github.com/go-spatial/tegola/blob/v0.7.0/provider/provider.go#L16