v0.9.10: adjusted to be published in appimage.github.io

Adjusted AppImage support for appimage.github.io

Release notes from 0.9.9:
This is essentially the same as the v1.0.0 version but adapted to compile with CSFML v2.4 and consequently to build on Ubuntu 18.04, in order to provide an AppImage compatible with a wide range of systems.

v0.9.9: adapted to build under Ubuntu 18.04

This is essentially the same as the v1.0.0 version but adapted to compile with CSFML v2.4 and consequently to build on Ubuntu 18.04, in order to provide an AppImage compatible with a wide range of systems.

First release: v1.0.0

Fully functional clone of the original 2048 game. Compared to the original, it only lacks tile animations and clickable buttons. On the other hand, it features theme switching on the fly and three board sizes in the same program.

Continuous build

Add building AppImage and making draft release (#2)

* Use branch name for VERSION
* Use ubuntu-20.04 for AppImage, since CSFML 2.5 not available at ubuntu-18.04