Idea: Add a URI to the License object for non-standard license support #64

As of version 0.1 it seems that License Objects are only fit to support licenses with an SPDX identifier. I'd like to suggest adding a URI property to facilitate the expression of non-standard licenses without an identifier.

While including the full license text is also an option, I feel that would waste a lot of bits, and that it's a reasonable expectation for users of a non-standard license to have said license available on the web. In fact, a URI is arguably more accessible than an SPDX ID.