Includes unit tests for conformance and speed.

SSSE3/CFLPredictTest:
4x4: C time = 2063 us, SIMD time = 313 us (~6.6x)
8x8: C time = 6656 us, SIMD time = 493 us (~14x)
16x16: C time = 24970 us, SIMD time = 1327 us (~19x)
32x32: C time = 59020 us, SIMD time = 5178 us (~11x)

AVX2/CFLPredictTest:
4x4: C time = 2052 us, SIMD time = 333 us (~6.2x)
8x8: C time = 6712 us, SIMD time = 513 us (~13x)
16x16: C time = 25292 us, SIMD time = 1023 us (~25x)
32x32: C time = 58994 us, SIMD time = 2828 us (~21x)

Change-Id: I08690a548be981ff10e184de468b9e0e691ee812