The existing package has a number of problems:
- Usage of powershell for adding content files: these files
  are no longer executed by nuget (IIRC, as of NuGet v3+)
- Since they are no longer run, not only does the sample .cs
  does not get injected, but neither does the target run at
  all since it's also the PS1 that did the injection of an
  MSBuild target.

The latter is unnecessary since NuGet already supports providing
targets via nugets. This is added by providing the new InjectModuleInitializer.targets
as part of the nuget package.

WRT to the sample content file, since it adds little value and
it will be tricky to maintain in a compatible way across content vs
contentFiles and packages.config vs project.json/PackageReference in
VS2015+, I think it's simply better to just improve the readme.txt.

After all, it's just a simple class with one method. No big deal copying
it from the readme after installing.

Remove all the cruft from the old-way, including:

- Make the csproj nicer by using SDK-style
- Use PackageReference for Mono.Cecil instead of checking in libs
- Remove the manually crafted .nuspec and and folder structure and
  let NuGet (SDK) Pack do its work instead
- Include a .props that allows third parties to invoke the tool by
  using $(InjectModuleInitializerTool)
- Update the .targets to make it incremental build friendly, and
  support strong named assemblies too
- Temporarily remove tests from project (this needs to go into
  another project, now that there is a free test runner that can
  be installed in Community (TestDriven.NET).
- Remove the embedded assembly hack for loading Cecil, since this
  is a standalone tool that can simply resolve its own assemblies
  from its local directory under \tools
- Account for minor changes in Cecil that require disposing the
  assembly and reading it in memory up-front.
- Bump version to 2.0.0 since there's quite significant changes,
  including not supporting the old .ps1 anymore.

Improving compatibility with VS2017 and .NETCore projects

Since the compiler won't sign the main assembly in that case either.