Added generic download command.

sbt> download org.scalaz:scalaz-core_2.11:7.1.0 io.argonaut:argonaut_2.11:6.1-M4
[info] Set current project to policy (in build file:/mirror/r/psp/policy/)
[info] Updating {file:/mirror/r/psp/policy/}root...
[info] Resolving com.github.julien-truffaut#monocle-core_2.11;0.5.0 ...
[info] downloading https://repo1.maven.org/maven2/io/argonaut/argonaut_2.11/6.1-M4/argonaut_2.11-6.1-M4.jar ...
[info]  [SUCCESSFUL ] io.argonaut#argonaut_2.11;6.1-M4!argonaut_2.11.jar (2046ms)
[info] downloading https://repo1.maven.org/maven2/com/github/julien-truffaut/monocle-core_2.11/0.5.0/monocle-core_2.11-0.5.0.jar ...
[info]  [SUCCESSFUL ] com.github.julien-truffaut#monocle-core_2.11;0.5.0!monocle-core_2.11.jar (991ms)
[info] Done updating.
scalaz-core_2.11              $IVY/org.scalaz/scalaz-core_2.11/bundles/scalaz-core_2.11-7.1.0.jar
scala-library                 $IVY/org.scala-lang/scala-library/jars/scala-library-2.11.2.jar
scala-parser-combinators_2.11 $IVY/org.scala-lang.modules/scala-parser-combinators_2.11/bundles/scala-parser-combinators_2.11-1.0.2.jar
scala-xml_2.11                $IVY/org.scala-lang.modules/scala-xml_2.11/bundles/scala-xml_2.11-1.0.2.jar
argonaut_2.11                 $IVY/io.argonaut/argonaut_2.11/jars/argonaut_2.11-6.1-M4.jar
monocle-core_2.11             $IVY/com.github.julien-truffaut/monocle-core_2.11/jars/monocle-core_2.11-0.5.0.jar
$IVY/org.scalaz/scalaz-core_2.11/bundles/scalaz-core_2.11-7.1.0.jar:$IVY/org.scala-lang/scala-library/jars/scala-library-2.11.2.jar:\
$IVY/org.scala-lang.modules/scala-parser-combinators_2.11/bundles/scala-parser-combinators_2.11-1.0.2.jar:\
$IVY/org.scala-lang.modules/scala-xml_2.11/bundles/scala-xml_2.11-1.0.2.jar:$IVY/io.argonaut/argonaut_2.11/jars/argonaut_2.11-6.1-M4.jar:\
$IVY/com.github.julien-truffaut/monocle-core_2.11/jars/monocle-core_2.11-0.5.0.jar
>
A rich way of obtaining ScalaInstances.
Culling the herd.
Version incrementer in moduleid.

This is libsbt 0.4.6.