Map header macros and misc comments

Before:
```
NewBarkTown_SecondMapHeader: ; 0x94dd8
	; border block
	db $5

	; height, width
	db NEW_BARK_TOWN_HEIGHT, NEW_BARK_TOWN_WIDTH

	; blockdata (bank-then-pointer)
	dbw BANK(NewBarkTown_BlockData), NewBarkTown_BlockData

	; script header (bank-then-pointer)
	dbw BANK(NewBarkTown_MapScriptHeader), NewBarkTown_MapScriptHeader

	; map event header (bank-then-pointer)
	dw NewBarkTown_MapEventHeader

	; connections
	db WEST | EAST

	; WEST to Route 29
	db GROUP_ROUTE_29, MAP_ROUTE_29 ; connected map (group, id)
	dw (Route29_BlockData + ROUTE_29_WIDTH - 3) ; strip pointer
	dw $c830 ; strip destination
	db 9, ROUTE_29_WIDTH ; (connection strip length, connected map width)
	db 0, ((ROUTE_29_WIDTH * 2) - 1) ; yoffset, xoffset
	dw ($C807 + 59) ; window

	; EAST to Route 27
	db GROUP_ROUTE_27, MAP_ROUTE_27 ; connected map (group, id)
	dw (Route27_BlockData) ; strip pointer
	dw $c83d ; strip destination
	db 9, ROUTE_27_WIDTH ; (connection strip length, connected map width)
	db 0, 0 ; yoffset, xoffset
	dw ($C807 + ROUTE_27_WIDTH) ; window
; 0x94dfc
```

Now:
```
	map_header_2 NewBarkTown, NEW_BARK_TOWN, $5, WEST | EAST ; 0x94dd8

	; WEST to Route 29
	map ROUTE_29
	dw (Route29_BlockData + ROUTE_29_WIDTH - 3) ; strip pointer
	dw $c830 ; strip destination
	db 9, ROUTE_29_WIDTH ; (connection strip length, connected map width)
	db 0, ((ROUTE_29_WIDTH * 2) - 1) ; yoffset, xoffset
	dw ($C807 + 59) ; window

	; EAST to Route 27
	map ROUTE_27
	dw (Route27_BlockData) ; strip pointer
	dw $c83d ; strip destination
	db 9, ROUTE_27_WIDTH ; (connection strip length, connected map width)
	db 0, 0 ; yoffset, xoffset
	dw ($C807 + ROUTE_27_WIDTH) ; window
; 0x94dfc
```