Another new PC-demo

I have created a new version of the Itch.io-exclusive PC demo of Numbertron.

It fixes a very silly bug that I have somehow introduced this year, where the game didn't properly deselect tiles when for instance the refresher item becomes active. This could for instance cause that a move would register as lethal when it was not (it would be carried out properly, though).

It also changes the way golden hearts work, and introduces a new way of getting them. They are now used mainly to build temporary score multipliers. This is a brand new feature that required some rearranging of the user interface (and is probably not the kind of thing one should introduce this late in development, but I feel it works well).

There are also some small fixes and improvements. Backgrounds: Simple Stars looks better as the colours are no longer awful, and there is some progression there (inspired by Tempest 2000). Binary works better with certain blocks.