Use leaf in overview

Author: garydgregory

src/main/javadoc/overview.html

@@ -27,7 +27,7 @@
     You can find the Javadoc package list at the <a href="#all-packages-table">bottom of this page</a>.
   </p>
   <section>
-    <h1>Binary Encoders</h1>
+    <h1><img src="../images/leaf.svg" style="height: 1em; padding-right:0.25em" alt="leaf">Binary Encoders</h1>
     <p>Interfaces and classes used by the various implementations in the sub-packages.</p>
     <table>
       <caption>Binary Encoders</caption>
@@ -82,7 +82,7 @@ <h1>Binary Encoders</h1>
     </table>
   </section>
   <section>
-    <h1>Digest Encoders</h1>
+    <h1><img src="../images/leaf.svg" style="height: 1em; padding-right:0.25em" alt="leaf">Digest Encoders</h1>
     <p>
       <strong>WARNING:</strong> Some of the functions in this package might not be suitable for cryptography, or are no longer cryptographically-secure.
     </p>
@@ -152,7 +152,7 @@ <h1>Digest Encoders</h1>
     </table>
   </section>
   <section>
-    <h1>Language Encoders</h1>
+    <h1><img src="../images/leaf.svg" style="height: 1em; padding-right:0.25em" alt="leaf">Language Encoders</h1>
     <table>
       <caption>Language Encoders</caption>
       <tr>
@@ -190,7 +190,7 @@ <h1>Language Encoders</h1>
     </table>
   </section>
   <section>
-    <h1>Network Encoders</h1>
+    <h1><img src="../images/leaf.svg" style="height: 1em; padding-right:0.25em" alt="leaf">Network Encoders</h1>
     <table>
       <caption>Network Encoders</caption>
       <tr>