Organize the engine/ directory, director's cut

Cleaned up `engine/routines`, in favor of moving files into more
appropriate directories. predef-related routines are now in top-level
`engine`.
`rtc/delete_save_change_clock.asm` has been split into both
`menus/delete_save.asm` and `rtc/reset_password.asm`.

Made a new subdirectory:
* engine/math: Contains all generic math-related routines.

engine/rtc/reset_password.asm

@@ -257,40 +257,3 @@ ClockResetPassword: ; 4d41e
 	dec c
 	jr nz, .ComponentFromString
 	ret
-
-_DeleteSaveData: ; 4d54c
-	farcall BlankScreen
-	ld b, SCGB_DIPLOMA
-	call GetSGBLayout
-	call LoadStandardFont
-	call LoadFontsExtra
-	ld de, MUSIC_MAIN_MENU
-	call PlayMusic
-	ld hl, .Text_ClearAllSaveData
-	call PrintText
-	ld hl, .NoYesMenuHeader
-	call CopyMenuHeader
-	call VerticalMenu
-	ret c
-	ld a, [wMenuCursorY]
-	cp $1
-	ret z
-	farcall EmptyAllSRAMBanks
-	ret
-
-.Text_ClearAllSaveData: ; 0x4d580
-	; Clear all save data?
-	text_jump UnknownText_0x1c564a
-	db "@"
-
-.NoYesMenuHeader: ; 0x4d585
-	db 0 ; flags
-	menu_coords 14, 7, SCREEN_WIDTH - 1, TEXTBOX_Y - 1
-	dw .MenuData
-	db 1 ; default option
-
-.MenuData: ; 0x4d58d
-	db STATICMENU_CURSOR | STATICMENU_NO_TOP_SPACING ; flags
-	db 2 ; items
-	db "NO@"
-	db "YES@"

engine/rtc/restart_clock.asm

@@ -1,5 +1,4 @@
-
-ResetClock_GetWraparoundTime: ; 20000 (8:4000)
+RestartClock_GetWraparoundTime: ; 20000 (8:4000)
 	push hl
 	dec a
 	ld e, a
@@ -152,7 +151,7 @@ RestartClock: ; 20021 (8:4021)
 
 .pressed_up
 	ld a, [wBuffer1]
-	call ResetClock_GetWraparoundTime
+	call RestartClock_GetWraparoundTime
 	ld a, [de]
 	inc a
 	ld [de], a
@@ -164,7 +163,7 @@ RestartClock: ; 20021 (8:4021)
 
 .pressed_down
 	ld a, [wBuffer1]
-	call ResetClock_GetWraparoundTime
+	call RestartClock_GetWraparoundTime
 	ld a, [de]
 	dec a
 	ld [de], a
@@ -230,7 +229,7 @@ RestartClock: ; 20021 (8:4021)
 
 .PlaceChars: ; 20168 (8:4168)
 	push de
-	call ResetClock_GetWraparoundTime
+	call RestartClock_GetWraparoundTime
 	ld a, [wBuffer3]
 	dec a
 	ld b, a