Added FF46 in the memory map io range table (#639)

* Added FF46 in the memory map io range table

This is previously categorized under $FF40 -> $FF4B as LCD registers which is not correct. Pulled it out so it is more obvious.

* Sort start column

Author: shuhaowu

src/Memory_Map.md

@@ -30,6 +30,7 @@ $FF0F   |         |       DMG      | [Interrupts](<#FF0F — IF: Interrupt flag>
 $FF10   |  $FF26  |       DMG      | [Audio](<#Audio Registers>)
 $FF30   |  $FF3F  |       DMG      | [Wave pattern](<#FF30–FF3F — Wave pattern RAM>)
 $FF40   |  $FF4B  |       DMG      | LCD [Control](<#FF40 — LCDC: LCD control>), [Status](<#FF41 — STAT: LCD status>), [Position, Scrolling](<#LCD Position and Scrolling>), and [Palettes](<#Palettes>)
+$FF46   |         |       DMG      | [OAM DMA transfer](<#OAM DMA Transfer>)
 $FF4C   |  $FF4D  |       CGB      | [KEY0](<#FF4C — KEY0/SYS (CGB Mode only): CPU mode select>) and [KEY1](<#FF4D — KEY1/SPD (CGB Mode only): Prepare speed switch>)
 $FF4F   |         |       CGB      | [VRAM Bank Select](<#FF4F — VBK (CGB Mode only): VRAM bank>)
 $FF50   |         |       DMG      | [Boot ROM mapping control](<#Power-Up Sequence>)