Added area kwarg to mask.to_surface

[Matiiss]

Close #661
(I don't think any of that renaming mentioned there is going to happen, so, adding the area kwarg is about all there's left to it)

[MyreMylar]

Should the size of the area rectangle also be used to determine the size of the final surface created here - where no surface is provided?

It feels a bit odd to effectively ask for a chunk of a mask to be turned into a surface and then get more than that chunk back.

[MyreMylar]

Going to approve this, despite my slight quibbles about functionality as I think it will work either way. How it currently works is more similar to the .blit() version of the area parameter -but it does feel more logical to produce a cropped mask surface if we aren't explicitly supplying a surface.

[Matiiss]

Going to approve this, despite my slight quibbles about functionality as I think it will work either way. How it currently works is more similar to the .blit() version of the area parameter -but it does feel more logical to produce a cropped mask surface if we aren't explicitly supplying a surface.

I did use .blit()'s implementation as a reference, it made sense for this to be consistent with that at the time.