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/run-es2015.test.js

@@ -0,0 +1,21 @@
+'use strict';
+
+const fs = require('fs');
+const assert = require('assert');
+const mkdirp = require('mkdirp').sync;
+const runUtils = require('./run-utils');
+const pug = require('../');
+
+var cases = runUtils.findCases(__dirname + '/cases');
+var es2015 = runUtils.findCases(__dirname + '/cases-es2015');
+
+mkdirp(__dirname + '/output-es2015');
+
+describe('test cases for ECMAScript 2015', function() {
+  try {
+    eval('``');
+    es2015.forEach(runUtils.testSingle.bind(null, it, '-es2015'));
+  } catch (ex) {
+    es2015.forEach(runUtils.testSingle.bind(null, it.skip, '-es2015'));
+  }
+});