Determine which target frameworks to build for and update build definition.

[alphaleonis]

[HugoRoss]

And .NET 4.0.3

[alphaleonis]

Original title: Add builds targetting .NET 4.6, 4.6.1 and 4.6.2.

Determine which target frameworks to actually build for. Is there any advantage to create spearate versions for all the various target frameworks if we're not actually using any feature exclusive to them, or would it suffice with eg .NET 4.5.2 and netstandard2.0? (Might be a reduction in dependencies in net471... either way, investigate and determine this).