Cleanup Fragment Cache Plugin

[johnregan3]

Source Task: https://app.clickup.com/t/1pkb6h2

Updates:

• Standardize documentation and formatting throughout
• Rename index.php to the WP common practice of plugin-name.php format
• Add .gitignore, README.md and composer.lock
• Add Mindsize PHPCS file
• Use WP_Filesystem functions where it makes sense (Didn't pan out)

Next Steps:

• Flesh out README file with implementation instructions
• Remove composer as it only provides an autoloader / write new autoloader
• Instantiate classes as singletons to save resources
• Use namespaces to simplify class names and whatnot
• Write toolkit of helper functions to provide easy access for developers

Questions:

• How we can protect/escape the print() output in WP_Fragment_Cache::do()?