Fix image link in online docs

Author: Blake-Madden

docs/index.html

@@ -302,7 +302,7 @@ <h1 class="title">TinyExpr++</h1>
 </header>
 
 
-<p><img src="images/cover.png" title="TinyExpr++" class="quarto-cover-image nolightbox img-fluid"></p>
+<p><img src="manual/images/cover.png" title="TinyExpr++" class="quarto-cover-image nolightbox img-fluid"></p>
 <!-- Just want this preface in the gitbook.
      PDF output will have its own copyright page after the title.-->
 <p>This book is the guide to using the <em>TinyExpr++</em> library, a C++ formula parsing and evaluation system.</p>

docs/manual/_quarto.yml

@@ -22,8 +22,8 @@ book:
   output-file: "TinyExpr++ReferenceManual"
   language: en
   search: false
-  cover-image: "images/cover.png"
-  image: "images/cover.png"
+  cover-image: "manual/images/cover.png"
+  image: "manual/images/cover.png"
   navbar:
     logo: tinyexpr_logo.png
     right: