[FEATURE] Enforce Code standard

**Is your feature request related to a problem? Please describe.**
Everybody has the tendency to write code in a different way, which over the long run will make the code messy with different styles.

**Describe the solution you'd like**
Use a linter (or similar solution) to enforce (and potentially auto fix) any styling issues in such a way that it'll be the same style.
e.g [codesniffer](https://github.com/squizlabs/PHP_CodeSniffer) or [tlint](https://github.com/tighten/tlint)

**Describe alternatives you've considered**
n.t.b

**Additional context**
n.t.b

Compare the PHP_CodeSniffer and Tlint options named in the issue, then inspect the repository for existing PHP tooling and contribution checks. Define one enforceable coding standard, document how to run it and any auto-fix support, and verify that the project consistently passes the chosen check.

Written by the indexing model from the issue text.