Added Defines For RAM Sizes

[Rendaman13]

No description provided.

[ISSOtm]

I don't see the point of those equates, what would they be used for?

[Rendaman13]

It's particularly helpful for loops responsible for clearing memory.

For example

memclear::
 xor a
 ldi [hl],a
 dec bc
 ld a,b
 or c
 jr nz,memclear
 ret

clearVRAM::
 ld hl,_VRAM
 ld bc,_VRAM_SIZE ; This line looks more intuitive than "ld bc,$E000-$C000"
 call memclear

[ISSOtm]

Clearing VRAM isn't very useful, nor is WRAM - for the most part, those should be init'd separately. Also, ld bc, _SRAM - _VRAM makes as much sense, imo.