Workaround bugs in doc tools

Both Scaladoc and genjavadoc take exception to this project.

  - raw types in the generated mixin composition befuddle
    scaladoc (lodged as https://issues.scala-lang.org/browse/SI-8449)
  - implicit classes seem to mess up genjavadoc
  - as do private[pack] classes

Finally, I had to remove parameter documentation from the
`toJava` and `toScala` decorators, as the reference parameter
was the argument to the implicit conversion, not to the documented
method.

All said an done, we end up with:

 https://dl.dropboxusercontent.com/u/106552/genjavadoc-scala-java8-compat/genjavadoc-api/index.html

Review by @rkuhn. I'm still tossing up wheter to just code this in
Java (we'd have to drop or move the implicit conversions in that case.)