Rename xgboostclassifier.py to xgboost_classifier.py (TheAlgorithms#7550)

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: cclauss

DIRECTORY.md

@@ -461,7 +461,8 @@
   * [Similarity Search](machine_learning/similarity_search.py)
   * [Support Vector Machines](machine_learning/support_vector_machines.py)
   * [Word Frequency Functions](machine_learning/word_frequency_functions.py)
-  * [Xgboostclassifier](machine_learning/xgboostclassifier.py)
+  * [Xgboost Classifier](machine_learning/xgboost_classifier.py)
+  * [Xgboost Regressor](machine_learning/xgboost_regressor.py)
 
 ## Maths
   * [3N Plus 1](maths/3n_plus_1.py)
@@ -536,7 +537,7 @@
   * [Line Length](maths/line_length.py)
   * [Lucas Lehmer Primality Test](maths/lucas_lehmer_primality_test.py)
   * [Lucas Series](maths/lucas_series.py)
-  * [Maclaurin Sin](maths/maclaurin_sin.py)
+  * [Maclaurin Series](maths/maclaurin_series.py)
   * [Matrix Exponentiation](maths/matrix_exponentiation.py)
   * [Max Sum Sliding Window](maths/max_sum_sliding_window.py)
   * [Median Of Two Arrays](maths/median_of_two_arrays.py)
@@ -582,6 +583,7 @@
     * [P Series](maths/series/p_series.py)
   * [Sieve Of Eratosthenes](maths/sieve_of_eratosthenes.py)
   * [Sigmoid](maths/sigmoid.py)
+  * [Signum](maths/signum.py)
   * [Simpson Rule](maths/simpson_rule.py)
   * [Sin](maths/sin.py)
   * [Sock Merchant](maths/sock_merchant.py)
@@ -590,6 +592,7 @@
   * [Sum Of Arithmetic Series](maths/sum_of_arithmetic_series.py)
   * [Sum Of Digits](maths/sum_of_digits.py)
   * [Sum Of Geometric Progression](maths/sum_of_geometric_progression.py)
+  * [Sum Of Harmonic Series](maths/sum_of_harmonic_series.py)
   * [Sylvester Sequence](maths/sylvester_sequence.py)
   * [Test Prime Check](maths/test_prime_check.py)
   * [Trapezoidal Rule](maths/trapezoidal_rule.py)