Improve code on loadMetadata() to verify if class exists, avoid a later warning when calling class_parents()
Instead throws a \RuntimeException if class doesn't exists.
Improve code to fulfill coding standards.
Actions done:
- Change exception to MappingException
- Change test to use setExpectedException instead of @expectedException
- Update phpdoc of loadMetadata and fix CS
Improve CS
Merge pull request #274 from entering/load-metadata-avoid-warn-absent-class

Improve code on loadMetadata() to verify if class exists