Add checkbox images to app/images

This is the start of the process of fixing #80

Signed-off-by: Cruz Julian Bishop <cruzjbishop@gmail.com>
Add initial handling of Github task list checkboxes

Some more work is needed to render completed items.

References #80

Signed-off-by: Cruz Julian Bishop <cruzjbishop@gmail.com>
Modify transparency of checkbox images

Signed-off-by: Cruz Julian Bishop <cruzjbishop@gmail.com>
Change checkbox images to the correct size

This is the last image-related change.

Ref: #80

Signed-off-by: Cruz Julian Bishop <cruzjbishop@gmail.com>
Merge pull request #253 from CruzBishop/add-github-checkboxes

Add initial support github checkboxes