Updated typo in the readme file.

PHP is now 5.6 minimum and README reflects new project structure

Cleaned up README.md to point to current manual instance. Removed txt readme version to improve maintainability

- Update Readme to include details about unit testing

- Add .gitignore file
- Add `/tests/` directory and `.gitignore` files to .gitattributes's export-ignore functionality

Refactor tests to more standardised format

- Add PHPUnit to composer

- Update readme to include instructions for installing composer packages and running unit tests through said package
- Use composer's autoloader to include mPDF during unit tests
- Update gitignore so the vendor directory is excluded

Add links and fix tag formatting