Changed assembly names; Integrated ILMerge into PostBuild (...)

- Fody NuGet packages should have only one assembly at the root of the package. Ref: https://github.com/Fody/Fody/wiki/DeployingAddinsAsNugets
- Stamp depends on LibGit2Sharp.
- To use LibGit2Sharp when deployed in a Fody NuGet package, the assemblies should be merged. ILMerge (packaged here) is used for this.
- The process was done right before NuSpec packaging. I have moved it into a Post-Build step until we get a nice release system up.