Add ability to log metrics of a regression model

[aslotte]

Add the ability to pass in the evaluation result from a regression model and automatically log all values as key-value pairs

[mbrdev]

@aslotte, I'll give this one a go if you want to assign to me.

Edit: Just read through comments on #19 looks like it's probably not needed anymore.

[aslotte]

Thanks @mbrdev. It's possible that what we already have to track metrics is sufficient, but it would be awesome if you could have a look and see what we could be missing that's specific for the regression scenario (e.g. just like a ConfusionMatrix is specific for classification)

[Brett-Parker]

As a part of #186 I was looking to see if there was anything missing on the metrics side. I don't think there is for regression. The current method tracks most metrics well!

[aslotte]

Given that we think that we currently captures all values, I'm going to close this issue.