Readd changelogs to the doc

Author: james-d-mitchell

docs/Doxyfile

@@ -1013,7 +1013,10 @@ WARN_LOGFILE           =
 INPUT                  = "../include/libsemigroups" \
                          "../include/libsemigroups/detail" \
                          "../README.md" \
-                         "install.md"
+                         "install.md" \
+                         "changelog-v1.md" \
+                         "changelog-v2.md" \
+                         "changelog-v3.md" 
 
 # This tag can be used to specify the character encoding of the source files
 # that Doxygen parses. Internally Doxygen uses the UTF-8 encoding. Doxygen uses

docs/DoxygenLayout.xml

@@ -8,6 +8,9 @@
     <tab type="mainpage" visible="yes" title="" />
     <tab type="user" visible="yes" url="_HEADING_" title="Installation and Changelog" />
     <tab type="user" visible="yes" url="@ref md_install" title="Install" />
+    <tab type="user" visible="yes" url="@ref md_changelog-v3" title="changelog - version 3" />
+    <tab type="user" visible="yes" url="@ref md_changelog-v2" title="changelog - version 2" />
+    <tab type="user" visible="yes" url="@ref md_changelog-v1" title="changelog - version 1" />
     <tab type="user" visible="yes" url="_HEADING_" title="Data structures" />
     <tab type="usergroup" visible="yes" url="@ref adapters_group" title="Adapters">
       <tab type="usergroup" visible="yes" url="[none]" title="No default implementation">