Implement SIMD improvements, especially for dot products

Add test-simd test program for benchmarking and testing SIMD-accelerated
functions (currently dot product calculation).

Several improvements and additions to SIMD interface:

Provide a large number of optimized SIMD variants for dot product
calculation. As it turns out, packed three-float vectors such as
Vector3D are hard to accelerate using SIMD, with non-SIMD versions
often being faster. An attempt has been made to provide better
SIMD performance for packed Vector3D, and a SIMD unpacking function
has been added as as well as a combination with transposition for
dot product functions.

In practice, it is probably best to require padded 16-byte
structures for Vector3D arrays that are used in SIMD calculation.
This is easily accomplished either by adding padding (possibly in a
subclass) or using an aligment directive (Vector3D DST_ALIGNED(16)).

Rename simd128_select_float to simd128_replicate_float.

Add work-in-progress SIMD acceleration for ARM NEON (dstSIMDNEON.h).

Signed-off-by: Harm Hanemaaijer <fgenfb@yahoo.com>