libstfinv [DOC]: mark non-implemented engines

Three of five engines are not yet implemented and only drafted in the source
code. This now is made clear in the comments to the declaration of engine
classes and in the group of engines.

src/libs/libstfinv/doxygen.txt

@@ -106,6 +106,22 @@ processing are described in the \ref page_help.
 
 \defgroup group_engines Engines
 
+All engines provide a common API. 
+They inherit this API from stfinv::STFBaseEngine.
+The library thus can be extended by additional approaches without the need to
+modify client programs.
+Currently implemented engines are made available through
+stfinv::STFEngine which serves as a handle class.
+The actual implementation to be used is selected in
+stfinv::STFEngine::initialize by means of a parameter string provided by the
+client.
+
+\note
+Not all engines classes for which drafts are available in the code are
+actually fully implemented.
+Only engines provided in stfinv::STFEngine::initialize should be considered as
+operational.
+
 \todo
   A detailed description for implementers is still missing
 

src/libs/libstfinv/stfinvfinitecausal.h

@@ -32,6 +32,13 @@ namespace stfinv {
   /*! \brief Engine to find a finite, causal source time-history in time domain
    * \ingroup group_engines
    *
+   * \attention
+   * This engine is not yet implemented.
+   * The concept of the approach is drafted in the comments to the class
+   * declaration. 
+   * As long a stfinv::STFEngineFiniteCausal is not made available through
+   * stfinv::STFEngine::initialize it must be regarded as a stub.
+   *
    * \par Concept behin this engine
    *
    * - \f$d_l\f$: data samples

src/libs/libstfinv/stfinvfixedstf.h

@@ -45,6 +45,12 @@ namespace stfinv {
 
   /*! \brief Engine to provide a fixed wavelet
    * \ingroup group_engines
+   *
+   * \attention
+   * This engine is not yet implemented.
+   * As long a stfinv::STFEngineFixedWavelet is not made available through
+   * stfinv::STFEngine::initialize it must be regarded as a stub.
+   *
    */
   class STFEngineFixedWavelet: public stfinv::STFFourierDomainEngine {
     public:

src/libs/libstfinv/stfinvnormalize.h

@@ -47,6 +47,14 @@ namespace stfinv {
   /*! \brief Normalization engine
    * \ingroup group_engines
    *
+   * \attention
+   * This engine is not yet implemented.
+   * The concept of the approach is drafted in the comments to the class
+   * declaration. 
+   * However this approach is under debate and might not even work properly.
+   * As long a stfinv::STFEngineNormalize is not made available through
+   * stfinv::STFEngine::initialize it must be regarded as a stub.
+   *
    * \par Motivation
    * On the down-side of Fourier domain least squares as is implemented
    * in stfinv::STFEngineFDLeastSquares is the least squares approach.