Cleanup parameter list of `ScriptedTests`.

All of `sbtVersion`, `defScalaVersion` and `buildScalaVersions` were
not used anymore. According to @harrah they are coming from really
old days of sbt and are not needed because of changes to how sbt
interacts with different Scala versions.
Further refinements to Scala version handling

- override location of resolved Scala jars when scalaInstance is unmanaged
- document current behavior: scalaHome, update, scalaInstance, autoScalaLibrary, managedScalaInstance
Docs: fix typo
initial 0.13 change summary
Docs: fix typo
API documentation in Extracted
remove deprecated Extracted.evalTask
move Eval test to correct location
Docs: note that plugins are loaded in a parent loader of build code
Allow cleanKeepFiles to contain directories

The directory contents will be kept as will empty directories.
Fix incremental compilation problem with package objects inheriting from invalidated sources in a subpackage.

Resolution of https://issues.scala-lang.org/browse/SI-4695 seems to be to deprecate
inheriting from a class in a subpackage.  This commit is an alternative solution,
possibly to be reverted or restricted if resolution of SI-4695 changes or if this
proves to be too conservative in practice.

Review by @gkossakowski.  With separate inheritance/function call dependency tracking,
this probably should only pull in package objects with inheritance dependencies on
invalidated files.
Multi-line prompt text offset issue (ticket #625)
minor cleanup of previous commit: var->val in sbt.JLine
add fix for #620 to the 0.12.2 changes page
use 2.10.0 final
ivy version 2.3.0-rc1 in documents
Docs: for 0.13 change summary, put in ignored toctree, link from Changes, fix subsection title
build: disable API/SXR generation until SI-6812 is resolved
fix credentials for publishing
use provisionally published sbinary