Add build for Web Assembly SIMD

[eshaz]

Add builds that support Web Assembly SIMD. This should significantly speed up decoding.

• Must be backwards compatible with browsers that don't support this feature, since it relatively new.
  • Could use feature detection and fall back to the non-SIMD build if not available.
• Update configure options to allow any SIMD optimized code to be added during pre-processing.
• The deinterleave function may be able to be optimized to use SIMD to more quickly iterate over the data, potentially by creating a custom function for this build. https://github.com/WebAssembly/simd/blob/master/proposals/simd/SIMD.md