Prefer structs over classes
Merge branch 'master' into jspahrsummers-patch-1
Fill in “structs over classes” section
Replace “interface reuse” with “polymorphism”
Merge pull request #8 from github/jspahrsummers-patch-1

Prefer structs over classes
Merge branch 'master' into jspahrsummers-patch-2

Conflicts:
	README.md
Rewrite as “make classes final by default,” expand it