Run retrolamba in process

[evant]

Should be able to invoke retrolamba directly instead of running it in a separate processes passing command line args. This can improve performance and possibly simplify implementation. It should start out disabled by default behind a flag such as

retrolambda {
  runInProcess true
}

to help iron out any issues.

Ideally we'd want to keep allowing the user to specify what version of retrolamba is used, but the mechanism might have to change.