v0.0.19: Play together online

The host can now remove a player: KICK in the lobby or in pause > PLAYERS, with a confirm. The removed player is sent home with a message and can't rejoin that game.
Mute anyone: MUTE in the lobby or in pause > PLAYERS hides that player's chat on your screen until you leave the game.
Teammates can upgrade each other's towers (the one who upgrades pays); only the builder can sell.
Frost Surge is now a team vote (press Y or N), and only the builder can switch off a Shield Wall's field.
The Base can only be sold when no enemies are coming, and the "I Can Read" achievement needs a finished tutorial (with fireworks).
Winning the tutorial now shows its victory camera and fireworks before the results screen (hosts saw the results at once).
Slowed enemies wear a lighter coat of frost, and the Cryo Mage's orb swirls with violet light.
The Hollow's records wall reads clearly: NIGHTS HELD and "WE KEEP THEIR LAMPS LIT" are now painted lettering.
Safer saves: if a save file is locked by another program (antivirus, a sync tool), your newest progress is kept and picked up the next time you start, and a damaged file is always copied aside before anything is written.