**Problem**
sbt 2.x uses crossTarget by default, but it contains Scala version
even when crossPaths is false.
**Solution**
This replaces it with the letter "u" for unspecified.
This flips the default `:=` operation to the cached task.
To opt out of the cache, use `Def.uncached(...)` or
mark the key with `@cacheLevel(include = Array.empty)`
**Problem**
`run` task has been emulated via function call inside of a sandboxed classloader,
and blocking the command processing of sbt server loop.
This poses isolation and availability issues.
**Solution**
This implements client-side run where the server creates a sandbox environment, and sends the information to the client,
and the client forks a new JVM to perform the run.
The client-side behavior has been implemented in sbtn side already.
For the details about this PR, please see the blog post https://eed3si9n.com/sbt-remote-cache/.
* Add cache basics
* Refactor Attributed to use StringAttributeMap, which is Map[StringAttributeKey, String]
* Implement disk cache
* Rename Package to Pkg
* Virtualize packageBin
* Use HashedVirtualFileRef for packageBin
* Virtualize compile task
kenji yoshida
Eugene Yokota
João Ferreira