Using pyyaml > 3.12 breaks tests

[mpsonntag]

The new release of pyyaml 4.1 breaks tests, there seem to be incompatibilities between the pyyaml versions.

[mpsonntag]

It seems, that with the new release of pyyaml 4.1 most python objects are no longer serialized by default and old yaml files containing python object specific code can no longer be easily loaded. This change has been introduced since this addresses an issue where potentially harmful code would have been executed when loading a yaml file. Check here for details.

Our two main problems with this are:

• pyyaml < 4.1 files cannot be easily be loaded now since they still contain serialized odML python objects e.g. !!python/object/apply:odml.dtypes.DType or python 2 derived !!python/unicode tags.
• datetime.time values can not be saved, since this serialization currently does not seem to be supported by pyyaml while the serialization of datetime.date and datetime.datetime still works fine.