Metric write up coming soon

I've taken my time with the Metric piece as it covers quite a few ideas.

All things going well, I will do the write up in the next day or so.

Also, I will update the PDFs.

Importantly, I want to add some of this information to the Advanced Doc.

I will add Proper Time which is pretty important and the Metric.

I will also add Gauss and the Gradient.