Updated the documentation and restructured a bit because it wasn't

compiling (note: Breathe not working)

doc/source/specialvalues.rst

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+==============
+Special values
+==============
+
+
+NA values
+=========
+
+All OBITypes have an associated NA (Not Available) value. 
+NA values are implemented by specifying an explicit NA value for each type, 
+corresponding to the R standards as much as possible:
+
+* For the type ``OBIInt_t``, the NA value is ``INT_MIN``.
+
+* For the type ``OBIBool_t``, the NA value is ``2``.
+
+* For the type ``OBIIdx_t`` and ``OBITaxid_t``, the NA value is ``SIZE_MAX``.
+
+* For the type ``OBIChar_t``: the NA value is ``\0``.
+
+* For the type ``OBIFloat_t``::
+
+    typedef union
+    {
+        double value;
+        unsigned int word[2];
+    } ieee_double;
+    
+    static double NA_value(void)
+    {
+        volatile ieee_double x;
+        x.word[hw] = 0x7ff00000;
+        x.word[lw] = 1954;
+        return x.value;
+    }
+
+
+Minimum and maximum values for ``OBIInt_t``
+===========================================
+
+* Maximum value : ``INT_MAX``
+* Minimum value : ``INT_MIN(-1?)``
+
+
+Infinity values for the type ``OBIFloat_t``
+===========================================
+
+* Positive infinity : ``INFINITY`` (should be defined in ``<math.h>``)
+* Negative infinity : ``-INFINITY``
+
+
+NaN value for the type ``OBIFloat_t``
+=====================================
+
+* NaN (Not a Number) value : ``NAN`` (should be defined in ``<math.h>`` but probably needs to be tested)