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.

.gitignore

@@ -1,5 +1,6 @@
 _*/
-
+dist-newstyle/
+site
 .ds_store
 .vscode/
 *.sage.py