Add functionality to determine source points from a model path

[alex-davies]

Still a work in progress

Requires

• More testing around differnet model layouts (e.g. relationship and attribute dictionaries, links, JObjects)
• More testing on netstandard1.0 (there is a shim in place, but needs to be tested that it works)
• Update readme with details of new functionality

Would also like to investigate further

• Way to convert from sourcePointer to model expression (i.e. reverse conversion)

[jonnii]

I thin you can target netstandard2.0 it's the defacto default now

[jonnii]

@codecutout sorry for the comment spam - github was having issues and posted a bunch of duplicates.

[alex-davies]

@jonnii is there a benefit in targeting netstandard2.0 if we are not using any of the additional API definitions?

my understanding was that the netstandards are backward compatible and only define the API contracts. So a netcoreapp2.x should be able to use a netstandard2.0 library just as easy as a netstandard1.5 library

[jonnii]

The only real benefit that I've come across of targeting netstandard2.0 is that it reduces the reference spam for anyone using net461 and the old csproj tooling. Now that .NET Core 2.1 is LTS I (personally) don't see the point in targeting anything less - it's things like shimming TypeInfo which I'd want to do without.