Support setting package versions in SDK projects

This release updates support for SDK (i.e. cross-targeting) projects so that package versions are also set the same way as assembly versions.

VS2017 SDK-based build support

Nerdbank.GitVersioning can successfully perform its functions on the SDK builds of .NET assemblies.

It can't yet influence the version of nuget packages that are built with the new SDK's Pack target. #93 tracks progress on this.

Install from NuGet

For folks not familiar with these new project types, they look like this:

<Project Sdk="Microsoft.NET.Sdk" ToolsVersion="15.0">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFrameworks>netcoreapp1.0;net46</TargetFrameworks>
    <RuntimeIdentifier>win7-x86</RuntimeIdentifier>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="**\*.cs" />
  </ItemGroup>
  <ItemGroup>
    <PackageReference Include="Nerdbank.GitVersioning" Version="1.5.61" />
    <PackageReference Include="Microsoft.NETCore.App" Condition=" '$(TargetFramework)' == 'netcoreapp1.0' " Version="1.0.1" />
  </ItemGroup>
</Project>

First "stable" release

This has been a gradual evolution. But we finally feel we've got critical mass of useful features and stable track record to have our first official release.

Release candidate for first stable build

Fixes

#25 Always include git commit ID in nuget package versions except when built with /p:publicrelease=true
#26 MSBuild AssemblyVersion property should always have 4 integer components bug

Install via NuGet

Barring any blocking bugs being found, this is expected to be the last RC. The next release should be a stable NuGet package.