Check for function additions

[dsyme]

Some functions have been added to Fsharp.Core on recent times

We should check they have corresponding fluent versions here

[cartermp]

I have a branch adding some that were recently added.

The base FSharp.Core this uses is 4.5.2. So we can't add anything before then unless we want to change the package version. Since it's a view over FSharp.Core itself, we're naturally constrained by reach vs. APIs.

[dsyme]

I think technique is

1. Complete for FSharp.Core 4.5.2, then publish
2. Complete for FSharp.Core 4.7.2, then publish
3. Complete for FSharp.Core 5.0.0, then publish

This package is so simple and stable it will be ok for the 4.7.2 users to rely on the 2nd version etc. We can take this approach now versioning and nuget for FSharp.Core is properly sorted