Emit SPDX-normalised license identifiers

[pmonks]

It would be awesome if lein-license were to emit SPDX normalised license identifiers, in addition to the raw text of the license. Right now the same license can be represented in the output in different ways, making downstream processing more difficult.

[arr-ee]

https://github.com/technomancy/lein-licenses#license-name-normalisation was built for this exact reason. You are more than welcome to contribute a list of SPDX synonyms.