Implement config adapters and beginning of Caddyfile adapter

Along with several other changes, such as renaming caddyhttp.ServerRoute
to caddyhttp.Route, exporting some types that were not exported before,
and tweaking the caddytls TLS values to be more consistent.

Notably, we also now disable automatic cert management for names which
already have a cert (manually) loaded into the cache. These names no
longer need to be specified in the "skip_certificates" field of the
automatic HTTPS config, because they will be skipped automatically.

modules/caddyhttp/fileserver/staticfiles.go

@@ -48,8 +48,6 @@ type FileServer struct {
 	Hide       []string `json:"hide,omitempty"`
 	IndexNames []string `json:"index_names,omitempty"`
 	Browse     *Browse  `json:"browse,omitempty"`
-
-	// TODO: Content negotiation
 }
 
 // Provision sets up the static files responder.
@@ -83,7 +81,7 @@ func (fsrv *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request, _ cadd
 
 	filesToHide := fsrv.transformHidePaths(repl)
 
-	root := repl.ReplaceAll(fsrv.Root, "")
+	root := repl.ReplaceAll(fsrv.Root, ".")
 	suffix := repl.ReplaceAll(r.URL.Path, "")
 	filename := sanitizedPathJoin(root, suffix)
 
@@ -302,7 +300,7 @@ func calculateEtag(d os.FileInfo) string {
 	return `"` + t + s + `"`
 }
 
-var defaultIndexNames = []string{"index.html"}
+var defaultIndexNames = []string{"index.html", "index.txt"}
 
 var bufPool = sync.Pool{
 	New: func() interface{} {