Enhance documentation with SEO metadata and layout

Added a new custom layout template for SEO and social media meta tags. Updated multiple documentation files with metadata for improved search engine optimization and social sharing. Enhanced Sphinx configuration with additional HTML options and meta tags.

docs/_templates/layout.html

@@ -0,0 +1,45 @@
+{% extends "!layout.html" %}
+
+{% block extrahead %}
+  {{ super() }}
+  <!-- Additional SEO and social meta tags -->
+  <meta name="application-name" content="tzst">
+  <meta name="generator" content="Sphinx {{ sphinx_version }}">
+  
+  <!-- Schema.org markup for search engines -->
+  <script type="application/ld+json">
+  {
+    "@context": "https://schema.org",
+    "@type": "SoftwareApplication",
+    "name": "tzst",
+    "description": "A Python library for creating and extracting tar.zst archives with high performance and comprehensive features",
+    "applicationCategory": "DeveloperApplication",
+    "operatingSystem": "Cross-platform",
+    "programmingLanguage": "Python",
+    "license": "https://opensource.org/licenses/MIT",
+    "url": "https://xixu-me.github.io/tzst/",
+    "downloadUrl": "https://pypi.org/project/tzst/",
+    "softwareVersion": "{{ version }}",
+    "author": {
+      "@type": "Person",
+      "name": "Xi Xu"
+    },
+    "offers": {
+      "@type": "Offer",
+      "price": "0",
+      "priceCurrency": "USD"
+    }
+  }
+  </script>
+
+  <!-- Canonical URL for better SEO -->
+  {% if pagename != 'index' %}
+  <link rel="canonical" href="https://xixu-me.github.io/tzst/{{ pagename }}.html">
+  {% else %}
+  <link rel="canonical" href="https://xixu-me.github.io/tzst/">
+  {% endif %}
+  
+  <!-- Preconnect to external domains for performance -->
+  <link rel="preconnect" href="https://fonts.googleapis.com">
+  <link rel="preconnect" href="https://cdnjs.cloudflare.com">
+{% endblock %}