Missing c++ compiler requirement

[Benny-]

Reppy is not a pure python project. It would be helpful if the readme listed the extra compiler requirements (for all relevant operating systems, and with links) in the installation section.

[b4hand]

Could you give me examples of such build requirements for other projects? I'm not sure exactly what you are asking for in the README. Also, if you happen to know the answer already, I'm happy to take a pull request.

[Benny-]

For examples. "Requires a fully compliant c++11" environment. I have reports it fails to properly compile on OSX (including the latest version).

unordered_map is used, which is in the c++11 spec.

[Benny-]

And another windows user reported "Build tools for visual c++ 2015 (v14)" was required before reppy was able to compile. See https://github.com/Benny-/Yahoo-ticker-symbol-downloader/issues/46