Tksheet

Fixed:
- [202](https://github.com/ragardner/tksheet/issues/202)

Fixed:
- [201](https://github.com/ragardner/tksheet/issues/201)
- The ends of grid lines were incorrectly displaying connections with one another when only showing horizontal or vertical grid
- When a cell dropdown and a row checkbox were in the same cell both would be drawn but only one would function, this has been changed to give dropdown boxes priority
- Index text overlapping checkbox when alignment is `"right"`/`"e"`/`"east"` and index is not wide enough

Added:
- [200](https://github.com/ragardner/tksheet/issues/200)

Fixed:
- Error when zooming or using `see()` with empty table
- Add initialization option `zoom` which is an `int` representing a percentage of the font size, `100` being no change

Removed:
- Some unnecessary internal variables

Added:
- Zoom in/out bindings control + mousewheel
- Zoom in bindings control + equals, control + plus
- Zoom out binding control + minus

Fixed:
- Bug with `format_row` using "all"

Fixed:
- 2 pixel misalignment of index/header and table when scrolling
- Undo cell edit not scrolling window

Added:
- Functionality to scroll multiple Sheets when scrolling one particular Sheet