Consistent cropping

[benlubas]

After this change we'll have consistent cropping behavior that follows these rules:

• If an image is not mounted on a window & buffer it shouldn't be resized/cropped at all, the API user should have full control.
• For images that are attached to a window and buffer it should behave the same and crop images at the window bounds, images should not be resized depending on scroll position.

Something of note, the existing get_global_offsets function defines the "bounds" of a window to exclude the sign column. This is helpful for placing image inline with text (you don't often want to cover the sign column). But this does mean it's harder to draw over a sign column of a specific window (which is something another plugin might want to do). This is just another thing that we might consider turning into an option in v2.0.0

screen_cap.mp4

Another note. In order to get this behavior I set my max_height_window_percentage to math.huge. Otherwise it shrinks the image and you can't see the crop happen on resize.

This finally (I hope) closes #42

This also fixes the issue where the markdown integration draws images over the status bar, but doesn't prevent an image from being drawn on the status bar if it's not bound to a window

[benlubas]

Ahhh, the cropping doesn't work with borders at the moment, let me take a look at that

fixed in 602cff9 & 620f557

[3rd]

Sorry for the slow turnover, thanks again for the great work!

[benlubas]

Not a problem at all, you've been awesome to work with!