Migrated to SDL2.
Added AppData.
Additional points for high altitude pod grabs, and lander snatches.
Shields defanged, super shield powerup gives killer shields.
Landers/crazies and crawlers are scaled as levels increase.
Landers can change altitude.
Made laser range more reasonable.
Added missle powerup, searcheds out landers attacking pods.
Limited number of lives and smartbombs.
Boss difficulty scales upward.
Merged saucer boss into unified boss system.
All objects save bullets explode now, still nonkilling.
Added death explosions, nonkilling, for player only so far.
Added saucer boss, level 4.
Added crawlers, which can shoot and are affected by all weapons.  No pod interaction.
Added static markers on ground for frame of reference.
Added laser (Z) powerup.
Saved individual high score.
Title screen.
Only saved pods respawned for 4 levels.
Copyright info.
Tripleshot, shield, life, smartbomb powerups.
Landers don't fire while chasing pods.
Implemented triple shot.  Needs powerup to activate.
Implemented shields. Replenished by level-up.
Implemented Smartbombs. Replenished by level-up.
Radar now wraps properly.
Landers will now ignore or abort chasing dead or rescued pods.
Landers grab pods, kill them, go crazy.
Crazies chase player.
Landers -> crazies if all pods are dead and none are in.
Made logo
Landers respawn, too.
Fixed pause, respawn
Landers shoot diagonally.
Landers shoot hozizontally, move.  Can kill you and a carried pod.
Added landers, shootable, collidable, and game over logic.
Deprecated pod_check() in favor of check_collision()
Can shoot pods.
Started bullet work
Put pods in a struct array.
Animated gate.
Basic gravity.
