add slugs table
create slug on word_set create

add rake task to create slugs for existing word_sets
prove word_set#to_slug uses latest slug
create slug on word_set update if any word changed
301 redirect number id routes to slug value
Merge branch 'master' into seo/50-slugs

Conflicts:
	app/controllers/word_sets_controller.rb
301 redirect older slugs to the newest slug
update share buttons to use slug instead of id
add better meta descriptions

also add “include” paths for each letter
fix typo
Merge pull request #50 from TSMMark/seo/50-slugs

SEO: Generate human-readable url path slugs for homophone sets