Initial commit of array-based sets

Arrays are so annoying...
Initial commit of quick array merge algorithm
Reworked QuickArrayMerge to not use a builder

The result size is always m+n, so a builder is useless and wasteful
Updated QuickArrayMergeCheck with a check that counts comparisons

a/b vs. b/a
Added manual test for QuickArrayMerge that attempts to find a worst case
Moved CountingOrder into test namespace
Implemented IntervalSeq using the array merge operation
Implemented tests for IntervalSeq

Also implemented benchmark
Implemented some more operations, and enabled some more tests
Got coverage of IntervalSeq to 100%
Added IntervalSeqAlgebra and tests

Brought coverage to 100% again by explicitly checking xor
Renamed IntervalSet to IntervalTrie

Also renamed supporting classes, and renamed IntervalTrie to Tree. Added
some annotations to make scalastyle pass.
Added build coverage to generic branch
Removed println from tests
Added spire implicits to sbt console
Removed generic branch from travis.yml