Include links to Scala standard library types in generated Scaladoc

[xirc]

Closes #73

sbt provides the autoAPIMappings option.

https://www.scala-sbt.org/1.x/docs/Howto-Scaladoc.html#Enable+automatic+linking+to+the+external+Scaladoc+of+managed+dependencies

Set autoAPIMappings := true for sbt to tell scaladoc where it can find the API documentation for managed dependencies. This requires that dependencies have this information in its metadata and you are using scaladoc for Scala 2.10.2 or later.

Before

After

[SethTisue]

LGTM, thank you!