Add license-expression library

[steven-esser]

To support #90, we should add the https://github.com/nexB/license-expression library to DeltaCode and update our algorithm to use this library.

[Pratikrocks]

@MaJuRG , @johnmhoran could you explain a bit more about the context of this issue , In what terms will we use this library ?

[johnmhoran]

Hi @Pratikrocks . The scan files produced by https://github.com/nexB/scancode-toolkit contain a number of fields, including license_expression. Our goal is to find a way for DeltaCode -- which compares two ScanCode-Toolkit result files -- to compare and score pairs of simplified license expression values, and we'll need the https://github.com/nexB/license-expression library to do more detailed comparisons.

[Pratikrocks]

Thanks @johnmhoran for the explanation

[Pratikrocks]

I was thinking to integrate license-expresiion library to deltacode in the following manner::

We would provide an option for the user in the command line to specify a license type (eg:MIT..,may be more than one),then based upon the choice we would show the deltas/print in json(or csv) file where either my old or new file has the license(s) specified by the user.

Moreover we could also provide another command line arguments to display if the deltas when explicitly new path has a license.

Actually in this way we can Implement many different queries based upon the license detection

I was planning to integrate this way .What are your views @MaJuRG , @johnmhoran regarding this

[steven-esser]

No, we just want the library for handling license_expression strings.

[Pratikrocks]

okay @MaJuRG ,this will be effective in detecting the licenses more proficiently, moreover some redundant methods could be reduced.