message: Update supported compiler versions in README
  Closes
diff: @@ -52,9 +52,9 @@ Supported Compilers
  The code is known to work on the following compilers:
  -- clang 3.5.2
  -- GCC 4.9.4 (C++14 support requires GCC 5.2; C++14 "extended constexpr" support is poor before 6.1.)
  -- VS2015 Update 3 "Clang with Microsoft CodeGen" (Clang/C2)
  +- clang 3.6.2 (or later)
  +- GCC 4.9.4 (or later) (C++14 support requires GCC 5.2; C++14 "extended constexpr" support is poor before 6.1.)
  +- "Clang with Microsoft CodeGen" (Clang/C2) VS2015 Update 3 (or later)
  **Development Status:** This code is fairly stable, well-tested, and suitable for casual use, although currently lacking documentation. No promise is made about support or long-term stability. This code *will* evolve without regard to backwards compatibility.
  