Merge branch 'ExportGifsAtZoomScale'

Bump Goya version to v0.0.9a

Export gif animations at the current zoom level

Update README.md

Merge remote-tracking branch 'origin/AddAnimationSupport'

Update preview image for github readme

Bump Goya version to v0.0.8a

Add link to twitter page

Update default image to show basic animation example

Also respond to backspace key when deleting selections. Feels more natural

Ensure that current frame is valid after resizing canvas

Ensure new documents are fully transparent

Prevent backspace from triggering the browser's back button

Ensure that background color is drawn properly when exporting animations

Comment out code for exporting history animation