Added toto marks on the missing sections of the documentation

Update #110

doc/source/users_guide/dataspace.rst

@@ -188,8 +188,63 @@ STL container to obtain all simple dataspaces in a collection sdfsdfsf
                  {
                     return space.type() == Type::SIMPLE;
                  });
+                 
+Dataspace type trait
+====================
+
+When working with user defined types a new type trait to create a dataspace 
+must be provided if something else than a scalar dataspace should be 
+returned for this type. 
+
+As an example we consider here a trait for a 3x3 matrix type. The C++ class
+template for such a class could look like this 
+
+.. code-block:: cpp
 
+    template<typename T> class Matrix
+    {
+      private:
+        std::array<T,9> data_; 
+      public:
+      
+        T *data();
+        const T *data() const;
+    }; 
 
+Now as a dataspace for such a type we would like to have a simple dataspace 
+of shape 3x3 and fixed size. The type trait which must be provided could 
+look like this 
+
+.. code-block:: cpp
+
+    #include <h5cpp/hdf5.cpp>
+    
+    namespace hdf5 {
+    namespace dataspace {
+    
+    
+    template<> class TypeTrait<Matrix>
+    {
+      public:
+        using DataspaceType = Simple;
+        static DataspaceType create(const Matrix &)
+        {
+          return Simple({3,3});
+        }
+    
+        static void *ptr(Matrix &value)
+        {
+          return reinterpret_cast<void*>(value.data());
+        }
+    
+        static const void*cptr(const Matrix &value)
+        {
+          return reinterpret_cast<const void*>(value.data());
+        }
+    };
+    }
+    }
+    
 Selections
 ==========
 
@@ -228,8 +283,17 @@ To apply a selection you need to
 .. figure:: ../images/hdf5_selection_manager.svg
    :align: center
    :width: 75%
+
+.. todo:: finish this section
+
+Hyperslab selections
+--------------------
+
+.. todo:: write this section
+
+Point selections
+----------------
 
-Hyperslabs
-----------
+.. todo:: write this section
 
 

doc/source/users_guide/overview.rst

@@ -221,6 +221,10 @@ is used. As a matter of fact it is the job of the dataspace to map the
 multidimensional index of a particular element onto a linear address in the 
 storage area. 
 
+.. todo::
+
+    add a figure here!
+
 When data is written to disk, the content of the :cpp:class:`MemoryStorage` 
 is transfered to the :cpp:class:`DiskStorage`. It is important to note that 
 the dataspace of the latter one must not be equal to that of the memory storage. 
@@ -229,6 +233,10 @@ data elements in memory must be convertable to those associated with the
 file storage. The same is true for the other direction when reading data 
 from the disk. 
 
+.. todo::
+
+    add a figure here!
+
 Selections and partial IO
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -249,7 +257,7 @@ With a point selection we could for instance read the elements
 size 3 (which would be 72Bytes in total) or in a more sophisticated setup
 we could map them on points (0),(5) and (11) in a 1D array in memory. 
 
-
+.. todo:: add a figure here