Reduce Vector Monoid to be just O(n) for 2.10
Fix Monoid for IndexedSeq rather than Vector
Delete IndexedSeq instances and operations

Use Vector, where we can talk about complexity of all operations, rather
than just a couple.
Change Foldable toIndexedSeq to toVector
Add back in IndexedSeqTest as VectorTest
Merge pull request #792 from puffnfresh/feature/delete-indexedseq

Delete IndexedSeq instances and operations