Added STEP Part 21 (ISO 10303-21) support
Merge branch 'master' of github.com:adamjcook/highlight.js into adamjcook-master

Conflicts:
	AUTHORS.en.txt
	CHANGES.md
	docs/css-classes-reference.rst
	src/test.html
Add detection test for step21
Merge branch 'adamjcook-master'