v0.6.5

Mostly bugfixes and small gameplay tweaks. The main user-facing change is that you now get 4 choices on level-up instead of 3.

Laevis now depends on libtooltipmenu. You need to download both and load libtooltipmenu before Laevis.

• Change: renamed "Shots" to "Inscription" in elemental upgrades so the names make
  sense with (e.g.) melee weapons.
• Change: Explosive Death now has a brief delay before dealing explosive damage, so
  explosions visibily ripple outwards when a chain reaction is triggered.
• Change: Explosive Death's range now increases more slowly with levels, and is
  based on the radius of the exploding monster; bigger enemies produce bigger booms.
• Change: split the menu code into a separate library, libtooltipmenu.pk3
• Change: you can now pick between 4 upgrades when you gain a level
• Fix: upgrade generation can no longer take unbounded time if you're unlucky
• Fix: upgrade generation can no longer freeze the game if the pool of upgrade candidates is very small
• Fix: Added some missing sprites to the repo (they were still in the pk3 but not versioned)