Improve support for target frameworks

[pombredanne]

The target framework used when resolving a project file is the first of the target(s)
declared in the properties of the project.

A. We should document this behaviour
B. We should have a better way to deal with these

B.1 Either a possible command line option for the target framework :

• We could have an option that would need to be validated against declared frameworks values of a project
• We could accept any valid framework value?

B.2 Or resolve for all frameworks

• This would avoid a CLI option
• If we resolve for all frameworks, how would we report these?

C. in all cases we should find a proper way to store the target framework in the output:

I think this we should report these either as a dependency scope, as extra data or we should add new attributes to the package/dependency model to capture the general concept of a target OS/arch/platform where the combination of target framework and possible runtime id. This model change would need to be propagated to ScanCode Tookt and other inspectors.

[pombredanne]

We have a new command line argument to select a target-framework, named "--target-framework" and that will override the project-configured target: that's the B1. option.