splitSpaces: fix off by one error
add benchmark for splitSpaces
splitSpaces: shorter, more understandable algorithm (but slower?)
spliteSpaces: reduce preallocation
splitSpaces: make i loop local [trivial]
splitSpaces: use bytes.IndexByte
Revert "splitSpaces: use bytes.IndexByte"

This reverts commit 15fd4e9d5c542d3e5d1751fd6971f57c7c050f1a.