Neo 3 RC1 support

This preview adds Neo 3 RC1 support for Neo Express.

Note, as of Neo 3 preview 5, the Neo 3 project has updated to use .NET 5.0. As such, this version of neo-express requires .NET 5.0. Neo 2 compatible versions of neo-express will continue to use .NET Core 3.1.

As of preview 5, Neo Express has moved to a master/master-2.x branch structure that mirror other Neo project repos. Neo 2 compatible versions of neo express will be produced out of the master-2.x branch and will have major release numbers 1.x. Neo 3 compatible versions of neo express will be produced out of the master branch and will have major release numbers 2.x and/or 3.x. Both versions will use the package name Neo.Express, though the command line app name has been shortened from neo-express to neoxp as of this release.

Note, preview releases prior to preview 5 used a temporary naming scheme to differentiate it from the production Neo-express release. The package was named Neo.Express3 and the tool was named nxp3. As described at the time and above, these have changed to Neo.Express and neoxp as of this preview.

You can install this pre-release of Neo Express directly from NuGet.org by executing the following command at a terminal prompt. Note, the --version option is required since this is a preview release

> dotnet tool install -g Neo.Express --version 2.0.21-preview

Note, you can install any pre-release of Neo Express directly from the build server NuGet feed by executing the following command at a terminal prompt.

> dotnet tool install -g Neo.Express --add-source https://pkgs.dev.azure.com/ngdenterprise/Build/_packaging/public/nuget/v3/index.json --version <insert desired version here>