mattkretz/vir-simd: vir-simd 0.1.0

This is the first release of vir-simd, a header-only library to make the use of std::experimental::simd from the Parallelism TS 2 easier.

This release contains:

• A full implementation of ISO/IEC TS 19570:2018 Programming Languages — Technical Specification for C++ Extensions for Parallelism Section 9 "Data-Parallel Types".
• A mechanism to use the libstdc++ implementation transparently, when available.
• Extensions on top of stdx::simd:
  • additional casts
  • std::bitset and stdx::simd_mask conversions
  • bitwise operators for floating-point simd
  • simd concepts
  • micro-benchmarking helper functions specifically for stdx::simd
  • a preview of simdize type transformation