refactor: rename options for maps, search, and comments

Use provider names rather than integers.

BREAKING CHANGE:

- Rename `site.Params.comments.engine` to `site.Params.comments.provider`
- Rename `site.Params.search.engine` to `site.Params.search.provider`
- Rename `site.Params.map.engine` to `site.Params.map.provider`
- Use provider name (string) rather than integer
- For built-in search, provider is "wowchemy"
- For leaflet maps, the provider is "mapnik" or "mapbox"

.gitignore

@@ -10,6 +10,7 @@ node_modules/
 
 # Hugo
 resources/
+public/
 
 # Mac
 .DS_Store