Documentation & Logging cleanups.

1. Document the use of dogleg and a general discussion of
   trust region methods.
2. Added a TBD section on compiler/linker flags.
3. Summary::FullReport now prints out sparse_linear_algebra_library
   and trust_region_strategy_type.

Change-Id: I01f680070d510715900f345364855689005d54bb
diff --git a/internal/ceres/solver_impl.cc b/internal/ceres/solver_impl.cc
index 41b6d75..877a5af 100644
--- a/internal/ceres/solver_impl.cc
+++ b/internal/ceres/solver_impl.cc
@@ -203,6 +203,9 @@
   summary->num_residuals = problem_impl->NumResiduals();
 
   summary->num_threads_used = options.num_threads;
+  summary->sparse_linear_algebra_library =
+      options.sparse_linear_algebra_library;
+  summary->trust_region_strategy_type = options.trust_region_strategy_type;
 
   // Evaluate the initial cost and residual vector (if needed). The
   // initial cost needs to be computed on the original unpreprocessed