Doc: set the version from cmake

doc/libeisgenerator.doxygen.in

@@ -38,7 +38,7 @@ PROJECT_NAME           = @PROJECT_NAME@
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 1.0.x
+PROJECT_NUMBER         = @CMAKE_PROJECT_VERSION_MAJOR@.@CMAKE_PROJECT_VERSION_MINOR@.x
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a