Deprecation warning with new ruamel version

[LaurentBergeron]

At multiple location in the exdir package, yaml.safe_load is used. This syntax will be deprecated by Ruamel. Using ruamel 0.17.21, the following Deprecation warning appears:

PendingDeprecationWarning:
  load will be removed, use

    yaml=YAML(typ='safe', pure=True)
    yaml.load(...)

We should update this code base to use the new syntax