Retarget the solution to VS2019 Build tools (v142) to allow support for Visual Studio 2019, out-of-the-box.

Problem Statement
Developers cannot use Visual Studio 2019 to build this solution without installing older Visual Studio 2017 Build Tools (v141). These can be hard to find for the everyday dev, requiring you to go to MSDN downloads and search specifically for the required version.

Note: those Build Tools can be quickly found here.

Evidence or User Insights

Steps to Reproduce:

1. Clone this repo with only Visual Studio 2019 installed.
2. Attempt to Rebuild

=> You are not able to build, due to failed checks for the v141 Toolset

Proposal
Retarget the solution, which is literally a two-click process:

1. Open the Solution in Visual Studio 2019 and right click on the solution head
2. Select "Retarget" and click OK.

The default toolset version will be preselected as v142 by default.

Goals

• Stay in sync with Microsoft's vision of using modern tooling
• VS2019 is significantly faster to use than VS2017 (this is proven, not just anecdotal).

Considerations

This may affect developers who have not updated to Visual Studio 2019 yet if there's no backwards check in the toolcheck list. This can be mitigated by making sure v141 is still in the list after adding v142.