feat: add smartypants

- replace right arrow with unicode equivalent

scripts/smartypants.js

@@ -0,0 +1,48 @@
+const { escape } = require('marked/src/helpers');
+
+// https://github.com/markedjs/marked/blob/b6773fca412c339e0cedd56b63f9fa1583cfd372/src/Lexer.js#L8-L24
+// Replace dashes only
+const smartypants = (str) => {
+  return str
+    // em-dashes
+    .replace(/---/g, '\u2014')
+    // en-dashes
+    .replace(/--/g, '\u2013')
+    // opening singles
+    .replace(/(^|[-\u2014/(\[{"\s])'/g, '$1\u2018')
+    // closing singles & apostrophes
+    .replace(/'/g, '\u2019')
+    // opening doubles
+    .replace(/(^|[-\u2014/(\[{\u2018\s])"/g, '$1\u201c')
+    // closing doubles
+    .replace(/"/g, '\u201d')
+    // ellipses
+    .replace(/\.{3}/g, '\u2026')
+    // right arrow
+    .replace(/->/g, '\u2192');
+};
+
+hexo.extend.filter.register('marked:tokenizer', function(tokenizer) {
+  const { smartypants: isSmarty } = this.config.marked;
+  tokenizer.inlineText = function(src, inRawBlock) {
+    const { rules } = this;
+
+    // https://github.com/markedjs/marked/blob/b6773fca412c339e0cedd56b63f9fa1583cfd372/src/Tokenizer.js#L643-L658
+    const cap = rules.inline.text.exec(src);
+    if (cap) {
+      let text;
+      if (inRawBlock) {
+        text = cap[0];
+      } else {
+        text = escape(isSmarty ? smartypants(cap[0]) : cap[0]);
+      }
+      return {
+        // `type` value is a corresponding renderer method
+        // https://marked.js.org/using_pro#inline-level-renderer-methods
+        type: 'text',
+        raw: cap[0],
+        text
+      };
+    }
+  }
+});