docs: add security policy document

docs: add contributors file with contribution guidelines

docs: update README with backward difference and Helmert encoding

feat: add examples for Helmert and backward difference encoding

refactor: update encoding package with version and all encoding techniques

docs: add quick start guide for new users

feat: add installation validation script

test: add unit tests for encoding selector utility

feat: add example demonstrating automatic encoding selection

feat: add intelligent encoding technique selector based on data characteristics

feat: implement backward difference and Helmert encoding for ordered categorical variables

merge: resolve README conflict, keep comprehensive version

docs: update CHANGELOG with all new features and improvements

docs: add encoding decision tree and performance guide

test: add unit tests for WoE and Leave-One-Out encoding