Ingame Menu buttons, Deactivate Bugfix

fixed bug where movement occurred in the same step in which a menu
deactivates instances, causing player to move through walls whose
collision isn't being considered in that step; fixed bug where no weapon
would be found for processing collision in the same step in which a menu
deactivates instances; added functionality to ingame menu buttons
New Popup, Menu Pause Image

new art for popup menu; menus once again draw a pause image behind
themselves
New Descendable Platform Implementation

no longer relies on hacky removal of collision (which breaks for
everything that isn't the player); now tests the colliding character's
position relative to the colliding descendable platform
Movement & Wall Collision Polish

fixed descent while colliding with both a wall and a descendable
platform; fixed inconsistent x/y rounding; added correction to last good
position when needed
fix for "last good position" and slopes; enemy stub; enemy regen
Standard Enemy Collision

player can now collide with standard (sized/shaped) enemies; only "hard"
collision is horizontal; vertical collisions will "guide" player away,
and even if player remains "inside" the enemy, horizontal movements are
allowed out of the enemy (but not into the enemy)