Ipycanvas

New features:
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- Add support for color gradients 142
- Add support for patterns 143
- Add `fill_polygon` and `stroke_polygon` methods 151
- Add `stroke_lines` method 152

Improvements:
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- Reduce messages size 129
- Improve communication speed by using binary buffers only 132
- Implement sleep method 126

Improvements
- Added `ellipse` method for adding an ellipse to the current path
- Added `Path2D` class for drawing SVG paths
- Added `stroke_line` method for directly drawing a line without using a path
- Added `fill_circle` and `stroke_circle`, shorthands for full `fill_arc` and `stroke_arc`
- Added `RoughCanvas` for hand-drawn style

Big fixes
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- Fix mouse events for the MutliCanvas

Improvements

- Refactor sizing logic. The web canvas has two sizes, the colorbuffer size and the display size (actual size on the screen). We used to only expose the colorbuffer size and force the display size to be the same. The user can now control the display size through the `layout` property. 111 113

Improvements

- Ship `.d.ts` files with the JavaScript package 97
- Change `getCoordinates` and `resizeCanvas` from private to protected 98