Actually make a2x optional

We might not even write man pages tbh

CMake/Manpage.cmake

@@ -1,8 +1,9 @@
-find_package(A2X REQUIRED)
+find_package(A2X)
 
-add_custom_target(man ALL)
+if (A2X_FOUND)
+    add_custom_target(man ALL)
 
-function(add_manpage name section)
+    function(add_manpage name section)
         add_custom_command(
             OUTPUT ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/${name}.${section}
             COMMAND ${A2X_COMMAND}
@@ -28,4 +29,5 @@ function(add_manpage name section)
             DESTINATION ${CMAKE_INSTALL_FULL_DATAROOTDIR}/man/man${section}
             COMPONENT documentation
         )
-endfunction()
+    endfunction()
+endif()