Merge branch 'hotfix/57'

Close #57
[#70] lazy-load metadata instances

- Instead of pre-loading `Metadata` instances, create them only when
  they are retrieved. Change is 100% BC with previous version.
Updated QA tools

- Removed php-cs-fixer
- Added phpcs
Fixed CS errors/warnings flagged by phpcs
Merge branch 'hotfix/70' into develop

Forward port #70