Targets file integrated into buildGib, also multiple nuspec files.

* No longer is it necessary to edit the csproj file. All that is required
  is dropping in the NuGet package and editing the config file.
* Multiple nuspec files are supported now, so if a solution has more than
  one nuspec, each of them can keep in sync with version number.

Signed-off-by: William Raiford <bill.mybiz@gmail.com>