All the redundancy between the .nuspec file and the .csproj file (both express and implied) is now removed. With it, I fix a few bugs:
1. The generated nuspec file includes the developmentDependency tag that was in the project file but not the checked in file.
1. The package now applies to *all* projects regardless of their target framework (well, so long as they're .netstandard1.0 compatible) instead of all projects rejecting this package unless they targeted .NET Core 2.0 or higher.
I also moved the .targets file into a folder structure within the project that resembles where it will appear in the package. This makes it more obvious that it belongs to the package when looking at the source code, and makes it easier to maintain the build/ folder in the package going forward because all files in it are included.
Fixes#431
Marco Rossignoli