Use ruamel_yaml

Created by: Zaharid

I recently updated reportengine to use ruamel_yaml instead of pyyaml. It is better maintained and fixes some bugs I have seen in pyyaml (such as incorrectly parsing 1. as a string instead of a float). The crucial advantage is that it provides a way to get error messages with line numbers. It does have the disadvantage that its packaging situation is crazy: The pypi package uses some unholy setup that will slow down noticeably all your python scripts regardless of whether thy actually use the package. The conda package fixes that but the author of ruamel.yaml refused to merge the changes, and so the conda package ruamel_yaml is different from the pypi package ruamel.yaml. reportengine.compat abstracts away the difference.

Since this already works in reportengine, there is no reason it shouldn't work in validphys.