Documentation update.

1. Complete restructuring of the documentation to account for
   GradientProblemSolver.
2. Update the version history to account for changes since 1.9.0.
3. Add links and document the various examples that ship with ceres.
4. Documentation for GradientProblem GradientProblemSolver.

Change-Id: If3a18f2850cbc98be1bc34435e9ea468785b8b27

include/ceres/gradient_problem_solver.h

@@ -72,7 +72,6 @@ class CERES_EXPORT GradientProblemSolver {
       max_line_search_step_expansion = 10.0;
       max_num_iterations = 50;
       max_solver_time_in_seconds = 1e9;
-      num_threads = 1;
       function_tolerance = 1e-6;
       gradient_tolerance = 1e-10;
       logging_type = PER_MINIMIZER_ITERATION;
@@ -224,10 +223,6 @@ class CERES_EXPORT GradientProblemSolver {
     // Maximum time for which the minimizer should run for.
     double max_solver_time_in_seconds;
 
-    // Number of threads used by Ceres for evaluating the cost and
-    // jacobians.
-    int num_threads;
-
     // Minimizer terminates when
     //
     //   (new_cost - old_cost) < function_tolerance * old_cost;
@@ -251,13 +246,6 @@ class CERES_EXPORT GradientProblemSolver {
     // is sent to STDOUT.
     bool minimizer_progress_to_stdout;
 
-    // If true, the user's parameter blocks are updated at the end of
-    // every Minimizer iteration, otherwise they are updated when the
-    // Minimizer terminates. This is useful if, for example, the user
-    // wishes to visualize the state of the optimization every
-    // iteration.
-    bool update_state_every_iteration;
-
     // Callbacks that are executed at the end of each iteration of the
     // Minimizer. An iteration may terminate midway, either due to
     // numerical failures or because one of the convergence tests has
@@ -309,10 +297,10 @@ class CERES_EXPORT GradientProblemSolver {
     // Sum total of all time spent inside Ceres when Solve is called.
     double total_time_in_seconds;
 
-    // Time (in seconds) spent evaluating the residual vector.
+    // Time (in seconds) spent evaluating the cost.
     double cost_evaluation_time_in_seconds;
 
-    // Time (in seconds) spent evaluating the jacobian matrix.
+    // Time (in seconds) spent evaluating the gradient.
     double gradient_evaluation_time_in_seconds;
 
     // Number of parameters in the probem.