Factors exception hierarchy into reusable fragment.

The fragment with hyperlinks is included now from the system module.

doc/exception_hierarchy_fragment.txt

@@ -0,0 +1,31 @@
+* `E_Base <system.html#E_Base>`_
+  * `EAccessViolation <system.html#EAccessViolation>`_
+  * `EArithmetic <system.html#EArithmetic>`_
+    * `EDivByZero <system.html#EDivByZero>`_
+    * `EOverflow <system.html#EOverflow>`_
+  * `EAssertionFailed <system.html#EAssertionFailed>`_
+  * `EAsynch <system.html#EAsynch>`_
+    * `EControlC <system.html#EControlC>`_
+  * `EDeadThread <system.html#EDeadThread>`_
+  * `EFloatingPoint <system.html#EFloatingPoint>`_
+    * `EFloatDivByZero <system.html#EFloatDivByZero>`_
+    * `EFloatInexact <system.html#EFloatInexact>`_
+    * `EFloatInvalidOp <system.html#EFloatInvalidOp>`_
+    * `EFloatOverflow <system.html#EFloatOverflow>`_
+    * `EFloatUnderflow <system.html#EFloatUnderflow>`_
+  * `EInvalidField <system.html#EInvalidField>`_
+  * `EInvalidIndex <system.html#EInvalidIndex>`_
+  * `EInvalidObjectAssignment <system.html#EInvalidObjectAssignment>`_
+  * `EInvalidObjectConversion <system.html#EInvalidObjectConversion>`_
+  * `EInvalidValue <system.html#EInvalidValue>`_
+    * `EInvalidKey <system.html#EInvalidKey>`_
+  * `ENoExceptionToReraise <system.html#ENoExceptionToReraise>`_
+  * `EOutOfRange <system.html#EOutOfRange>`_
+  * `ESynch <system.html#ESynch>`_
+    * `EOutOfMemory <system.html#EOutOfMemory>`_
+    * `EResourceExhausted <system.html#EResourceExhausted>`_
+    * `EStackOverflow <system.html#EStackOverflow>`_
+    * `ESystem <system.html#ESystem>`_
+      * `EIO <system.html#EIO>`_
+      * `EOS <system.html#EOS>`_
+        * `EInvalidLibrary <system.html#EInvalidLibrary>`_