Export build.sbt values inside sbt.

* Expose the values PAST the Eval/sbt.compiler package.
* Find projects using the name API rather than finding htem and dropping all values immediately.
* Adds a test to make sure the .sbt values are discovered and set-able
* Expose .sbt values in Set command and inside BuildUnit methods.
* Ensure `consoleProject` can see build.sbt values.
* Add notes for where we can look in the build if we want to expose .sbt values between files.

Review by @eed3si9n 
I dunno.  I'd make it a lazy-val, but that's risky.  I think we need to figure out caching behind this (which may already exist).

AFAICT it's only called from `set` and/or `consoleProject`.