* object: refactored writer to detect split points before writing
This introduces new primitive that will be moved into splitters
themselves in subsequent commits. I'm doing this in small steps to
ensure we don't regress at any time.
* splitter: refactored TestSplitters test
This is use slow (byte-by-byte) and fast (nextSplitPoint) methods of
determining split points.
Note nextSplitPoint is not implemented by splitters yet, but this
verifies that the test is expecting the right thing.
* object: splitter refactoring - replaced ShouldSplit() with NextSplitPoint() everywhere, still not optimized
* splitter: added additional dimension to splitter_test
We split either in large chunks or one byte at a time to catch
the corner cases in the splitter implementation.
* splitter: optimized splitters using NextSplitPoint primitive
This improves splitter performance by about 40% (buzhash) and makes
it virtually free for FIXED splitter.