Add README and simplify ViewEngine API

- ViewEngine.init() no longer requires allocator
- render() and renderTpl() accept allocator parameter
- Remove deinit() - no resources to clean up
- Remove unused parse/renderDoc methods
- Add memory management guidance to runtime.zig
- Clean up unused imports and options

src/benchmarks/templates/simple-1.pug

@@ -0,0 +1,14 @@
+.simple-1(style="background-color: blue; border: 1px solid black")
+  .colors
+    span.hello Hello #{name}!
+      strong You have #{messageCount} messages!
+    if colors
+      ul
+        each color in colors
+          li.color= color
+    else
+      div No colors!
+  if primary
+    button(type="button" class="primary") Click me!
+  else
+    button(type="button" class="secondary") Click me!