NumericDiffCostFunction supports dynamic number of residuals.

1. Update AutoDiffCostFunction template parameters to be consistent
with NumericDiffCostFunction.

2. Update the documentation for NumericDiffCostFunction and
AutoDiffCostFunction.

Change-Id: I113038abb5bedebb0f6f326f2a4ac31480d785fc
diff --git a/docs/source/building.rst b/docs/source/building.rst
index c326fd1..b74a9dd 100644
--- a/docs/source/building.rst
+++ b/docs/source/building.rst
@@ -1,8 +1,8 @@
 .. _chapter-building:
 
-=====================
-Building Ceres Solver
-=====================
+============
+Installation
+============
 
 Stable Ceres Solver releases are available for download at
 `code.google.com <http://code.google.com/p/ceres-solver/>`_. For the