Update README
Fix and test for re-reading deepscanlines

Attempting to read the same scanline multiple times would fail, leaving FrameBuffer sampleCountSlice unchanged
Fix makes subsequent reads copy data from the internal cache to the framebuffer for efficiency.
Test provided in IlmImfTest
Merge branch 'develop' of https://github.com/openexr/openexr into devel
Added PartHelper functions and test
Updated CompositeDeepScanLine to multithread compositing steps

DeepCompositing objects must now be threadsafe when readPixels decodes multiple scanlines and threading is enabled
Added support for setting view in exrmultipart
Added missing break statement
Ported Autodesk optimisations
Merge branch 'develop' into iif-weta
Support converting scanline EXRs to multipart files using exrmultipart
Ported optimization test to IlmImfTest
optimization test uses namespace macro properly
Syncing over with ILM internal updates.
Fixed misinterpretation of dtex samples in deepopacity case, updated README, comments, and ChangeLog to reflect fix.
Merge branch 'develop' into iif-weta
Folding in the changes for switching on the availability of the SSE2 instruction set.

From Brendan Bolles (fnordware)

There are many options for Windows SSE2 flags, most of which are not
optimal. We'd rather have a false positive (possibly resulting in a
compiler error that we could then expore further) than a false negative.

_M_IX86_FP == 2 will tell you that the compiler flags are set to SSE2,
but they are often not set and SSE2 would still build properly if we
allow it.

_M_IX86 || _M_X64 would assume that all Intel CPUs had SSE2, but would
incorrectly include the headers on old versions of Visual Studio.

_MSC_VER >= 1300 seems to be the best test. This corresponds to Visual
Studio .NET 2002, the first version that had SSE2.

_M_CEE_PURE also must be off. Google it.
Added missing file
Added missing file.
Added isOptimizationEnabled() and test
fixed documentation typos, readPixelSampeCounts, documented rawPixelData deepscanline calls