set minimum required cmake version to 3.16.0 (fixes build warnings)

CMakeLists.txt

@@ -64,7 +64,7 @@ set (RELEASE_SERVICE_VERSION_MICRO "70")
 #############################################################################
 ### required versions                                                     ###
 
-CMAKE_MINIMUM_REQUIRED(VERSION 2.8.12 FATAL_ERROR)
+CMAKE_MINIMUM_REQUIRED(VERSION 3.16.0 FATAL_ERROR)
 
 # Honor visibility properties for all target types (since cmake 3.3)
 IF (POLICY CMP0063)

doc/devel.docbook

@@ -182,7 +182,7 @@
     	If you intend to compile &kwave; from the sources, you will need at least:
 	<itemizedlist>
 	    <listitem><para>
-		<ulink url="&url_cmake;">cmake</ulink>-2.8.12 or newer
+		<ulink url="&url_cmake;">cmake</ulink>-3.16.0 or newer
 	    </para></listitem>
 	    <listitem><para>
 		A recent C/C++ compiler. GCC-4.x works fine, some older and any