Update the lecture notes and add chapter about classes

lecture/lecture.tex

@@ -82,7 +82,7 @@ There are exercises every week to practice the C++ programming. During the semes
 \input{05_references}
 \input{06_arrays}
 \input{07_namespaces}
-%\input{08_classes}
+\input{08_classes}
 %\input{09_generics}
 %\input{10_functors}
 %\input{11_iterators}