archrelease: Accept multiple tags

This allows for releasing to multiple repositories with a single commit:

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$ archrelease community-{i686,x86_64}
copying trunk to community-i686...done
copying trunk to community-x86_64...done
releasing package...done
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Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>
Signed-off-by: Pierre Schmitz <pierre@archlinux.de>