Release version 0.5.1

Adds Nunjucks usage info

Merge pull request artstorm#10 from artstorm/feature/twitter-card

Feature/twitter card

Merge pull request artstorm#9 from artstorm/feature/open-graph

Feature/open graph

Bumps version to 0.4.1

Merge pull request artstorm#7 from artstorm/feature/options

Feature / options

Merge pull request artstorm#6 from artstorm/feature/title

Feature/title

Merge pull request artstorm#5 from artstorm/feature/page-title

Feature/meta robots

Merge pull request artstorm#4 from artstorm/feature/seo-tag

Feature/seo tag

Merge pull request artstorm#3 from artstorm/v0.3.0

V0.3.0