Return UV vector from Texture.transformUv method

[jayschwa]

This makes the method consistent with most other vector transformations, and will make it easier to include it in a chain of operations.

[WestLangley]

Thanks. If you are changing the API, then the docs need to be updated, too.

@looeee has been very helpful with that.

[Mugen87]

I think it's useful to merge this PR. Currently the method returns undefined which seems not very consistent.

BTW: The change for docs/api/textures/Texture.html is not 100% correct since the return type should be added at the method's title. It should look like this:

<h3>[method:Vector2 transformUv]( uv )</h3>

@jayschwa Still interested? 😉

[mrdoob]

Merged and fixed.

[mrdoob]

Thanks!