Add ability to set style on a per-use basis

[rfreedman]

Currently, it looks like style items, such as 'showCircle' and 'showHandles' can only be set via items in a Theme.

It would be nice to be able to set these on the Crop instance programatically. For instance, I may want to crop some things rectangularly (with 'showCircle' = false), and others as circles (with 'showCircle' = true).

For just the 'showCircle' attribute, perhaps an 'asCircle' method could be added, to go along with the existing 'asSquare' method?

[andrewsdv]

I also need to crop some kind of images with circular mask and some with a rectangular mask. It will be great to enhance the android-crop library with such an ability I think.