File-based response support & static server

- Clean up UniversalPath implementation
    - Use Readable/Writable types correctly for stream methods
    - Add .list() methods for getting child files

- Make Response body specify explicit types and support
  writing Readable streams to the body

- Create a static file server that supports directory listing

src/resources/views/static/dirlist.pug

@@ -0,0 +1,45 @@
+doctype html
+html
+    head
+        title Index of #{dirname}
+        style.
+            body {
+                font-family: Arial, sans-serif;
+            }
+
+            table {
+                border-collapse: collapse;
+                width: 100%;
+            }
+
+            td, th {
+                border: 1px solid #dddddd;
+                text-align: left;
+                padding: 8px;
+            }
+
+            tr:nth-child(even) {
+                background-color: #dddddd;
+            }
+    body
+        h1 Directory Listing
+        h2 #{dirname}
+        table
+            tr
+                th Name
+                th Type
+                th Size
+            tr
+                td 📂 
+                    a(href='..') ..
+                td Directory
+                td -
+            each entry in contents
+                tr
+                    td #{entry.isDirectory ? '📂 ' : ''}
+                        a(href='./' + entry.name) #{entry.name}
+                    td #{entry.isDirectory ? 'Directory' : 'File'}
+                    td #{entry.size}
+        if !config('server.poweredBy.hide', false)
+            hr
+            small retrieved at #{(new Date).toDateString()} #{(new Date).toTimeString()} | powered by <a href="https://extollo.garrettmills.dev/" target="_blank">Extollo</a>