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-0.pug

@@ -0,0 +1 @@
+h1 Hello, #{name}