fix: add scoped error logging for lexer/parser errors

- Add std.log.scoped(.pugz) to template.zig and view_engine.zig
- Log detailed error info (code, line, column, message) when parsing fails
- Log template path context in ViewEngine on parse errors
- Remove debug print from lexer, use proper scoped logging instead
- Move benchmarks, docs, examples, playground, tests out of src/ to project root
- Update build.zig and documentation paths accordingly
- Bump version to 0.3.1

tests/sample_data/pug/test/cases/html.html

@@ -0,0 +1,9 @@
+<ul>
+<li>foo</li>
+<li>bar</li>
+<li>baz</li>
+</ul>
+<!--build:js /js/app.min.js?v=1449104952939-->
+<!--endbuild-->
+<p>You can <em>embed</em> html as well.</p>
+<p><strong>Even</strong> as the body of a block expansion.</p>