Fix some Doxygen documentation,

• including fixes to the Doxygen configuration.

Note, with something like

    /// @{ 
    /// @name some name 
    /// Documentation of foo 
    void foo();
    ...
    /// @}

Doxygen sees the whole initial block of comments as documentation of the group. Thus, there should be at least one blank line between the group documentation and member documentation, or a different comment style should be used. That is, for example,

    /// @{ 
    /// @name some name 

    /// Documentation of foo 
    void foo();
    ...
    /// @}

or

    /** @{ 
        @name some name  */
    /** Documentation of foo */
    void foo();
    ...
    /** @} */