Now actually attempting to build levels on top
Starting on Unmerged merging scheme, and creating a place for Spark utility methods.
Unmerged merging scheme builds
Some production of upper-level shings is happening
Can reproduce a segfault due to baking empty IntervalMaps.
Fixed IntervalMap not to segfault when you try to bake it when it's empty
Unmerged merging scheme seems to work, but one of the tests in ReferenceStructureTests is nondeterministically failing.
Trying to see if intermittent failure is caused by incorrectly-built indexes