Use PHP_CodeSniffer instead of php-cs-fixer

- Due to constant breakages on the latter.
Fixed CS issues flagged by phpcs

- Added development autoloading strategies to composer.json
- Fixed too-long lines
- Fixed closure brace position
Added "Contributing" section to README

- Primarily to document phpcs arguments
Merge branch 'hotfix/code-sniffer'

Switched to phpcs from php-cs-fixer