added GitHub raw download link

Added new error checking.

Added shorthand item names for items that don't fit on a sign.
"Ebook", "enchanted_book"
"Eapple", "enchanted_golden_apple"
"Etable", "enchanting_table"
"Bmush", "brown_mushroom"
"MushStem", "mushroom_stem"
"mushStew", "mushroom_stew"
"Rmush", "red_mushroom"
"BmushBK", "brown_mushroom_block"
"RmushBK", "red_mushroom_block"
"Pand", "polished_andesite"
"mossCobble", "mossy_cobblestone"