This provides a bunch of SIMD intrinsic wrappers as a precursor to the SIMD printers.

The aim is that the SIMD printer can be agnostic regarding the particular vector architecture.

The design is based rather loosely on the proposal P0214R6 for C++ Parallelism TS 2. The transcendental function implementations are adapted from the existing SIMD architecture-specific code, which in turn are based on the Cephes library algorithms.

The custom CSS for the html documentation have been tweaked.