fw+doc: Renaming and extending limit extenstion

SimpleLimits now called PerOutFaceLimits.  Also, there is now
PerFibLimits that is inherited from PerOutFaceLimits and implements
additional check.

Also, this commit includes a couple of tricks to improve documentation
of templated classes (PerOutFaceLimits and PerFibLimits). Not ideal, but
much better than before.
diff --git a/model/ndn-face.h b/model/ndn-face.h
index 78c65a7..acb1c90 100644
--- a/model/ndn-face.h
+++ b/model/ndn-face.h
@@ -111,7 +111,7 @@
   ////////////////////////////////////////////////////////////////////
 
   /**
-   * \Brief Assign routing/forwarding metric with face
+   * \brief Assign routing/forwarding metric with face
    *
    * \param metric configured routing metric (cost) of this face
    */