Support mouse in addition to touch controls

[tobiasvl]

It would be cool if the touch controls, at least Seg16 and Seg16 Fill, worked with mouse input in addition to touch input.

For example, I've used Seg16 for 4x4 grid-based puzzle games in the past, which is a genre that lends itself well to being able to click the individual squares.

In addition, (at least in Chrome) an Octo game that's embedded in an itch.io game page won't accept keyboard input until the player has clicked inside the iframe. Accepting mouse clicks on a title screen, say, gives the player immediate feedback that they've done the right thing by attempting to click the embed.

[JohnEarnest]

@tobiasvl give these changes a spin.

[tobiasvl]

Works great, thanks!