Create array for enemy shots.

Move "memory layout" comments and definitions into memory.asm.

memory.asm

@@ -0,0 +1,48 @@
+; Memory layout:
+; 0000-000F: scratch space for functions.
+; 0010-0011: controller state of joypad #1.
+; 0012-0013: controller state of joypad #2.
+; 0014-0016: 24-bit counter of vblanks.
+; 0017-0019: RGB color values to use for background color, from [0-31].
+; 001A-001B: 16-bit pointer to next random byte.
+; [gap]
+; 0020-0021: (x, y) coordinates of player.
+; 0022: shot cooldown timer.
+; 0023: next-shot state.
+; [gap]
+; 0030-003F: (x, y) velocities of each of the 8 possible shot states.
+; 0040-009F: {sprite, x, y, x-velocity, y-velocity, unused} per player shot.
+;            If sprite is 0, the shot is disabled.
+; 00A0-00FF: As above, for enemy shots.
+; [gap]
+; Sprite table buffers -- copied each frame to OAM during VBlank, using DMA.
+; 1000-11FF: table 1 (4 bytes each: x/y coord, tile #, flip/priority/palette)
+; 1200-121F: table 2 (2 bits each: high x-coord bit, size)
+; 1220-12A0: scratch table. One byte per sprite for high x-coord & size.
+.define joy1 $10
+.define joy2 $12
+.define vBlankCounter $14
+.define backgroundRed $17
+.define backgroundGreen $18
+.define backgroundBlue $19
+.define randomBytePtr $1A
+.define playerX $20
+.define playerY $21
+.define shotCooldown $22
+.define nextShotState $23
+.define shotVelocityTable $30
+.define playerShotArray $40
+.define playerShotArrayLength 16
+.define enemyShotArray $A0
+.define enemyShotArrayLength 16
+.define shotSize 6
+
+.define numSprites 128
+.define spriteTableStart $1000
+.define spriteTable1Size $200
+.define spriteTable2Start $1200
+.define spriteTableSize $220
+.define spriteTableScratchStart $1220
+
+
+