Fixed wrong url for Style Guide in Contributing Guide
Adjust docblock of load_class()

refs c26b9ebb00e29be2e972fece3bcf73d33249a64b
Merge pull request #3055 from ilatif/develop

Fixed wrong url for Style Guide in Contributing Guide
Merge pull request #3056 from vlakoff/docblock

Adjust docblock of load_class()
[ci skip] Add a note to CI_Model::__get() (issue #3046)