CPack: Add NuGet support

Create a CPack generator that uses `nuget.exe` to create packages:

    https://docs.microsoft.com/en-us/nuget/what-is-nuget

NuGet packages could be easily produced from a `*.nuspec` file (running
`nuget pack` in the directory w/ the spec file).  The spec filename does
not affect the result `*.nupkg` name -- only `id` and `version` elements
of the spec are used (by NuGet).

Some implementation details:

* Minimize C++ code -- use CMake script do to the job. It just let the
  base class (`cmCPackGenerator`) to preinstall everything to a temp
  directory, render the spec file and run `nuget pack` in it, harvesting
  `*.nupkg` files...;

* Ignore package name (and use default paths) prepared by the base class
  (only `CPACK_TEMPORARY_DIRECTORY` is important) -- final package
  filename is a responsibility of NuGet, so after generation just scan the
  temp directory for the result `*.nupkg` file(s) and update
  `packageFileNames` data-member of the generator;

* The generator supports _all-in-one_ (default), _one-group-per-package_
  and _one-component-per-package_ modes.

1 files changed, 4 insertions, 0 deletions

diff --git a/Tests/CPackComponentsForAll/MyLibCPackConfig-OnePackPerGroup.cmake.in b/Tests/CPackComponentsForAll/MyLibCPackConfig-OnePackPerGroup.cmake.in
index ac65dc9..d41225d 100644
--- a/Tests/CPackComponentsForAll/MyLibCPackConfig-OnePackPerGroup.cmake.in
+++ b/Tests/CPackComponentsForAll/MyLibCPackConfig-OnePackPerGroup.cmake.in
@@ -18,6 +18,10 @@ if(CPACK_GENERATOR MATCHES "DragNDrop")
    set(CPACK_COMPONENTS_GROUPING "ONE_PER_GROUP")
 endif()
 
+if(CPACK_GENERATOR MATCHES "NuGet")
+   set(CPACK_NUGET_COMPONENT_INSTALL "ON")
+endif()
+
 #
 # Choose grouping way
 #