attempt to pre-render post detail on server side.
move server post detail render to lib/post.js.
move nunjucks init to lib/build.js.
added smoke test for post detail renderer.
replace duck-typing checks w/ process.browser checks.
refactor to remove all process.browser conditionals.
consolidate shared server/client selectors in page.js.
set <title> on server-side.
enforce DRY
added page.test.js, renamed function to ensureSingleton.
Merge pull request #25 from toolness/server-post-detail-render

Pre-render post detail on server side.