[doc] Additional documentation

doc/additionalDoc/a-features.h

+/**
+   \defgroup Filters
+ */

doc/additionalDoc/e-operators.h

+/**
+\page subp_operators Operators on signals
+
+\section subp_unitary_op Unitary Algebraic operators
+
+\subsection ssubp_unitary_op Vector selector
+
+This entity output a vector remapping an input vector 
+\f${\bf v}_{in}=[v_0,v_1,\cdots,v_n]\f$.
+It is realized by specifying bounds such as \f(${[i,j],[k,l]}f$),
+then the output vector will be the contanetion of the
+intervals extracted from the input vector:
+\f${\bf v}_{out}=[v_i,v_{i+1},\cdots,v_{j-1},v_{j},v_{k},
+v_{k+1},\cdots,v_{l-1},v_l]\f$
+For instance if we have an input vector
+such that: 
+\code[bash]
+1
+2
+3
+4
+5
+6
+7
+9
+10
+\endcode
+then specifying the bounds \f$(3,5)\f$ and \f$( 7,10\f$) will gives
+the following output vector
+\code[bash]
+3
+4
+7
+8
+9
+\endcode
+
+ */