Add XCode project generation

[dascandy]

[graph]

For all the generators maybe a good way is to parse cmake -G output for list of generators and just pass whatever is available or supplied into the evoke tool. That will make the other project generation posts duplicates.

[dascandy]

@graph strictly speaking you can use the cmake export now to create a cmake project, and then use cmake to generate xcode or MSVC projects. It would be much better though to both skip a step of conversion (as it loses information and adds workarounds) and to not rely on people having CMake.