fixed some mistakes in gpu docs

doc/gpu_data_structures.tex

@@ -10,4 +10,6 @@ Creates continuous matrix in GPU memory.
 \cvarg{cols}{Column count.}
 \cvarg{type}{Type of the matrix.}
 \cvarg{m}{Destination matrix. Will be only reshaped if it has proper type and area (\texttt{rows} $\times$ \texttt{cols}).}
-\end{description}
+\end{description}
+
+Matrix is called continuous if its elements are stored continuously, i.e. wuthout gaps in the end of each row.