Add option to convert between SPDX Spec versions

[goneall]

The underlying library supports converting between versions if you specify the version when creating the new SPDX document.

Unfortunately, there is no command line option to support this.

There are a couple possibilities:

• Add a new comment like "upgradeSpdxDocument" which will take the new version as a noption
• Add a --version option to the SPDX translator which will use the new version for the translated file

Note that the library only support upgrades, not downgrades.

[vargenau]

I would prefer to have the option named --spdxversion.

The --version option should return the version of tools-java. In most tools, the --version option returns the version of the tool.