- Simplify scroll thumb calculations
- Correct thumb position when dragging with mouse
- Support border OS parameters
- Use usize for OS borders, to explicitly only accept positive integers
- Get correct tab height when using fancy tab bar
- Correctly draw depending on tab bar position
- Adjust minimum thumb size to be 1/2 of a cell height, so it has consistent size across platforms and screen densities
Fixes#1525
Removes the dependency on knowing where the pane top/left position
is so that the line render routine could be used in more places.
Adjusts the tab bar and scroll bar positioning so that the tab bar
ignores window padding and is always flush with the top/bottom window
edge (full width as well), and that the scroll bar top/bottom respects
the tab bar position and height.
Add a more general dragging thingy and use that to know when we
are dragging splits or the scroll thumb.
Fixup scrollbar math, which didn't account for whether the tabbar
was shown and which might cause the scroll thumb to jump around
on first drag (resolves#568)
