Adds site metadata access to the API

app/views/api/v1/site/index.rabl

@@ -0,0 +1,14 @@
+object false
+
+node(:title) {Setting.site_title}
+
+node(:max_chars) {500}
+
+node(:links) do
+  {
+    t('about.learn_more') => url_for(about_more_url),
+    t('about.terms') => url_for(terms_url),
+    t('about.source_code') => "https://github.com/tootsuite/mastodon",
+    t('about.other_instances') => "https://github.com/tootsuite/mastodon/blob/master/docs/Using-Mastodon/List-of-Mastodon-instances.md",
+  }
+end