Verify data table sizes with table_width and assert_table_length macros

This was discussed in #706

It also uncovered some off-by-one issues with defining some constants.

A few structs now use rsreset/_RS to define their offset constants, as discussed in #739

data/moves/tmhm_moves.asm

@@ -3,6 +3,7 @@
 
 TMHMMoves:
 ; entries correspond to *_TMNUM constants (see constants/item_constants.asm)
+	table_width 1, TMHMMoves
 
 ; TMs
 n = 1
@@ -43,4 +44,6 @@ PURGE MOVE_FOR_MT
 n = n + 1
 endr
 
+	assert_table_length NUM_TM_HM_TUTOR
+
 	db 0 ; end