Updating elevate to support multiple visual studio versions

[jrepp]

These changes include a fix to a deprecated windows API and converts the build process over to use CMake. With CMake you have a simple build definition file ~10 lines that can support Visual Studio 2013, 2015, 2017, nmake, gmake etc.

CMake is a proven build generation system used by a growing array of C++ projects and tools.

Elevate is a wonderfully simple tool that solves this silly UAC problem on windows. I love the simplicity of it and I hope that these changes improve that simplicity and keep the tool relevant for future users.