Add Hakyll site generator and assets

Add site executable and Haskell modules (site.hs, ChaoDoc.hs,
SideNoteHTML.hs, Pangu.hs) to handle Pandoc/Hakyll compilation,
theorem/sidenote processing and CJK spacing. Add CSS, font files,
favicon, templates, Makefile, and a CSL bibliographic style. Update
.gitignore to ignore build artifacts.

templates/navbar.html

@@ -0,0 +1,5 @@
+<header class="no-print">
+    <nav>
+        <a href="/">Home</a>
+    </nav>
+</header>