Add lightning spell check

Makefile

@@ -225,7 +225,10 @@ check-whitespace: check-whitespace/Makefile check-whitespace/tools/check-bolt.c
 check-markdown:
 	@tools/check-markdown.sh
 
-check-source: check-makefile check-source-bolt check-whitespace check-markdown
+check-spelling:
+	@tools/check-spelling.sh
+
+check-source: check-makefile check-source-bolt check-whitespace check-markdown check-spelling
 
 full-check: check check-source
 

tools/check-spelling.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+git grep -iE 'l[ightn]{6}g|l[ightn]{8}g|ilghtning|lgihtning|lihgtning|ligthning|lighnting|lightinng|lightnnig|lightnign' -- . ':!tools/check-spelling.sh'
+if [[ $? == 0 ]]; then
+    echo "Identified a likely misspelling of the word \"lightning\" (see above). Please fix."
+    echo "Is this warning incorrect? Please teach tools/check-spelling.sh about the exciting new word."
+    exit 1
+fi