Improve Index javadoc
Add key list method to LongKeyDomain
Add mutable and immutable ID indexes to data structures (#428)
Deprecate old indexes (#428)
Add 2.0.5 release notes
Decrease noisiness of TaskGroupRunner
Don't uses executor in trainTest when thread count is 1

This is a bad attempt at #426 that just uses an independent loop to run tasks when the thread count is 1, avoiding the executor and the group runner alltogether.
Fix eval script MOJO error message
Update release notes for eval changes [skip ci]
Pin GPG plugin version
Bump release plugin version
release version 2.0.5
Set version to next SNAPSHOT
Merge branch 'release/2.0' into merge-2.0

Conflicts:
	lenskit-api/pom.xml
	lenskit-archetype-fancy-analysis/pom.xml
	lenskit-archetype-simple-analysis/pom.xml
	lenskit-core/pom.xml
	lenskit-data-structures/pom.xml
	lenskit-eval-maven-plugin/pom.xml
	lenskit-eval/pom.xml
	lenskit-groovy/pom.xml
	lenskit-integration-tests/pom.xml
	lenskit-knn/pom.xml
	lenskit-package/pom.xml
	lenskit-slopeone/pom.xml
	lenskit-svd/pom.xml
	lenskit-test/pom.xml
	pom.xml
	src/site/apt/releases/index.apt.vm