Fix typos and enable links (#109)

* chore: enable youtube link

* chore: correct typos in comments

Author: sutatoruta

BENCHMARK.md

@@ -129,5 +129,5 @@ small_vgicp          : APE=5.956 +- 2.725  RPE(100)=1.315 +- 0.762  RPE(400)=6.8
 
 [Code](https://github.com/koide3/small_gicp/blob/pybench/src/benchmark/odometry_benchmark.py)
 
-Processing speed comparison between small_gicp and Open3D ([youtube]((https://youtu.be/LNESzGXPr4c?feature=shared))).
+Processing speed comparison between small_gicp and Open3D ([youtube](https://youtu.be/LNESzGXPr4c?feature=shared)).
 [![small_comp](https://github.com/koide3/small_gicp/assets/31344317/7959edd6-f0e4-4318-b4c1-a3f8755c407f)](https://youtu.be/LNESzGXPr4c?feature=shared)

README.md

@@ -431,7 +431,7 @@ python3 src/example/basic_registration.py
 
 ## [Benchmark](BENCHMARK.md)
 
-Processing speed comparison between small_gicp and Open3D ([youtube]((https://youtu.be/LNESzGXPr4c?feature=shared))).
+Processing speed comparison between small_gicp and Open3D ([youtube](https://youtu.be/LNESzGXPr4c?feature=shared)).
 [![small_comp](https://github.com/koide3/small_gicp/assets/31344317/7959edd6-f0e4-4318-b4c1-a3f8755c407f)](https://youtu.be/LNESzGXPr4c?feature=shared)
 
 ### Downsampling

include/small_gicp/registration/optimizer.hpp

@@ -108,7 +108,7 @@ struct LevenbergMarquardtOptimizer {
         // Solve with damping
         const Eigen::Matrix<double, 6, 1> delta = (H + lambda * Eigen::Matrix<double, 6, 6>::Identity()).ldlt().solve(-b);
 
-        // Validte new solution
+        // Validate new solution
         const Eigen::Isometry3d new_T = result.T_target_source * se3_exp(delta);
         double new_e = reduction.error(target, source, new_T, factors);
         general_factor.update_error(target, source, new_T, &e);
@@ -150,7 +150,7 @@ struct LevenbergMarquardtOptimizer {
 
   bool verbose;              ///< If true, print debug messages
   int max_iterations;        ///< Max number of optimization iterations
-  int max_inner_iterations;  ///< Max  number of inner iterations (lambda-trial)
+  int max_inner_iterations;  ///< Max number of inner iterations (lambda-trial)
   double init_lambda;        ///< Initial lambda (damping factor)
   double lambda_factor;      ///< Lambda increase factor
 };