feat: doc.cls support for cover image

other perf: change the filename separator for image assets from "_" to "-".

Author: Mister-Kin

latex_templates/cls_style/cls_style.tex

@@ -5,6 +5,10 @@
     \DocumentTitle{文档标题测试}
     \DocumentSubtitle{文档副标题测试}
     \DocumentCreatedDate{2020-07-21}
+    \DocumentCoverImage{}
+    \DocumentCoverImageScale{0.2}
+    \DocumentCoverImageTopMargin{20ex}
+    \DocumentCoverImageBottomMargin{5ex}
 
     \LinkBlogPost{https://test.LinkBlogPost}
     \LinkBlogPostMirror{https://test.LinkBlogPostMirror}

latex_templates/cls_style_light/cls_style_light.tex

@@ -5,6 +5,10 @@
     \DocumentTitle{文档标题测试}
     \DocumentSubtitle{文档副标题测试}
     \DocumentCreatedDate{2020-07-21}
+    \DocumentCoverImage{}
+    \DocumentCoverImageScale{0.2}
+    \DocumentCoverImageTopMargin{20ex}
+    \DocumentCoverImageBottomMargin{5ex}
 
     \LinkPDF{https://test.LinkPDF}
     \LinkPDFAccessCode{docs}