Add spellcheck_test script (#5655)

tests/spellcheck_test

+#!/usr/bin/env ruby
+
+# This test checks for spelling errors and provides suggested changes.
+
+require_relative '../lib/const'
+require_relative '../lib/color'
+
+unless File.exist? "#{CREW_PREFIX}/bin/codespell"
+  puts "This test requires codespell.  Install with 'pip install codespell'.".lightred
+end
+
+# Check for spelling errors.
+Dir.chdir '../' do
+  system 'codespell'
+end