Add OSGi metadata to core jar

This PR adds OSGi metadata to the shapeless core JAR utilizing https://github.com/sbt/sbt-osgi/, which allows OSGi users to deploy Shapeless directly without having to manually modify the manifest. There is no impact to non-OSGi users.

The resulting manifest looks like:

    Export-Package: 
      shapeless.test
        uses
          scala.reflect.macros
          scala.reflect.api
          scala.runtime
          scala.collection.mutable
          scala.reflect
          scala
        version: 1.2.5.SNAPSHOT
      shapeless
        uses
          scala
          scala.collection
          scala.collection.mutable
          scala.reflect
          scala.runtime
          scala.collection.immutable
          scala.collection.generic
          scala.util
          scala.sys
        version: 1.2.5.SNAPSHOT
    Bundle-Version: 
      1.2.5.SNAPSHOT
    Manifest-Version: 
      1.0
    Tool: 
      Bnd-1.50.0
    Bundle-Name: 
      com.chuusai.shapeless.core
    Bnd-LastModified: 
      1367345629055
    Created-By: 
      1.6.0_45 (Apple Inc.)
    Bundle-ManifestVersion: 
      2
    Import-Package: 
      scala
        version: [2.10,2.11)
      scala.collection
        version: [2.10,2.11)
      scala.collection.generic
        version: [2.10,2.11)
      scala.collection.immutable
        version: [2.10,2.11)
      scala.collection.mutable
        version: [2.10,2.11)
      scala.reflect
        version: [2.10,2.11)
      scala.reflect.api
        version: [2.10,2.11)
      scala.reflect.macros
        version: [2.10,2.11)
      scala.runtime
        version: [2.10,2.11)
      scala.sys
        version: [2.10,2.11)
      scala.util
        version: [2.10,2.11)
    Bundle-SymbolicName: 
      com.chuusai.shapeless.core