Add comprehensive biomedical statistical tests with visualizations

Features:
- Comprehensive T-Tests (one-sample, two-sample, paired, Welch's) with clinical examples
- Chi-Square Tests (goodness of fit, independence, McNemar's) with medical applications
- Correlation Analysis (Pearson, Spearman, Kendall, matrix analysis) with assumption checks
- Professional visualizations for all tests with statistical annotations
- Power analysis and sample size considerations for study design
- Real-world biomedical examples and interpretations

Files added:
- biomedical/t_tests_comprehensive.r (800+ lines)
- biomedical/chi_square_tests.r (700+ lines)
- biomedical/correlation_analysis.r (600+ lines)
- Updated DIRECTORY.md with new biomedical tests

Testing:
- All functions tested with and without plotting
- Comprehensive error handling and input validation
- Educational demonstrations with clinical scenarios
- No external package dependencies (pure base R)

Author: Brijesh03032001

DIRECTORY.md

@@ -3,7 +3,10 @@
   * [Apriori](https://github.com/TheAlgorithms/R/blob/HEAD/association_algorithms/apriori.r)
 
 ## Biomedical
+  * [Chi Square Tests](https://github.com/TheAlgorithms/R/blob/HEAD/biomedical/chi_square_tests.r)
+  * [Correlation Analysis](https://github.com/TheAlgorithms/R/blob/HEAD/biomedical/correlation_analysis.r)
   * [Mann Whitney U Test](https://github.com/TheAlgorithms/R/blob/HEAD/biomedical/mann_whitney_u_test.r)
+  * [T Tests Comprehensive](https://github.com/TheAlgorithms/R/blob/HEAD/biomedical/t_tests_comprehensive.r)
   * [Wilcoxon Signed Rank Test](https://github.com/TheAlgorithms/R/blob/HEAD/biomedical/wilcoxon_signed_rank_test.r)
 
 ## Classification Algorithms