"kpm pack --no-source" should nupkg the main project

[ChengTian]

See #80
In an initial implementation #371 , if we do kpm pack --no-source, the sources of main project are still exported. In next step, we want to export main project as a nupkg as well.

@lodejard @davidfowl , before we enable users to nupkg the main project, two points need to be clarified:

1. @lodejard mentioned that we should enable users to specify the main package when they execute k run . I guess we can have something like
   k --main ./packages/MainProject.4.0.0.0 run?
2. k run cannot execute without project.json. Can I simply copy the project.json file to {PACK_OUTPUT_DIR}/packages/MainProject.4.0.0.0/project.json?

[davidfowl]

1. By name not path.
2. Or we change k to understand nupkg's as well as project.json

[ChengTian]

@davidfowl Changing k to understand nupkgs sounds better because, in this case, main packages have the same structure as common packages. Consistency is always good 😄

[ChengTian]

@davidfowl , I am trying to make k understand nupkgs as we discussed above. Although I can get name, version and most other information from .nuspec file, the "loader" we specify in project.json is missing in .nuspec.

Seems we have no way to preserve "loader" information in this approach, should I turn to the approach where we copy and paste project.json into main nupkg?

[ChengTian]

Had a discussion with @lodejard and @davidfowl and made the following design:

1. Add files pattern in project.json
   To make sure non-source-code contents (including views, config files and etc.) are preserved in packed output, we add a new key files into project.json and the value of files specifies the pattern of files we want to preserve. Then we can get the files we want to preserve in output by subtracting all other specified files (including source files, exclude files, ignored files, shared files, preprocess files and resource files) from files that match files pattern. The default value of files is the pattern **.*.
2. Structure of kpm pack --no-source output
   Assume we have an app MyApp with the following dir structure and MyApp depends on a NuGet package DependencyPackage.1.0.0.0.
   
   After we do kpm pack --no-source in the root dir of MyApp, we will get the following output
   
3. How to run the packed app
   In the output above, execute k --app-name MyApp run in output/packages/MyApp.0.1-beta-SNAPSHOT/root/