Reset too easy to do accidentally

[alexer]

Spacebar isn't mentioned in the how-to-play, but it resets the game without any confirmation.

Accidentally resetting a game that is going well sucks. I should know, since I found this feature by accidentally hitting spacebar while playing http://joppi.github.io/2048-3D/ with >370k points and close to getting a 32768 tile.

I propose mentioning the spacebar-reset-functionality in the how-to-play section and adding a confirmation dialog. (Or just removing the feature, reloading the page isn't that hard)

[gabrielecirulli]

Might introduce a replay icon if we merge game autosaving in localstorage.

[gabrielecirulli]

#75 closes this.