Environment variable DUB_PACKAGE_VERSION added

[andre2007]

The new environment variable DUB_PACKAGE_VERSION can be used in shell / batch scripts called from "preGenerateCommands". The version of the package can be written to module file.
This would simplify e.g. this logic https://github.com/dlang/dub/blob/master/build.cmd

Is a unit test needed for the new environment variable?

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[PetarKirov]

When I read the the title I thought that this was exposing the version of dub itself and not of the currently compiled package. I think a more descriptive name would be DUB_PACKAGE_VERSION - would you mind renaming it to that?

[andre2007]

@ZombineDev done:)

[wilzbach]

Nice, but needs a PR to dub-docs before it can be merged.

[wilzbach]

This will be a lot nice than e.g. this hack here: https://github.com/dlang-community/D-Scanner/blob/master/dub.json#L27

[WebFreak001]

well it will sadly not be enough to fix it recompiling every time just yet, but useful nevertheless.

[andre2007]

Documents update dlang/dub-docs#7

PING :)