Updated the cmake to add the headers to project files + install target

[SeleDreams]

I've updated the cmake to add the install target and to add the headers to project files to easily edit them technically I think the visual studio project files and the makefiles aren't required anymore as the cmake can auto-generate them.

also I think that now WORLD could be submitted to the ubuntu and other distributions package managers as libWORLD if it isn't already, it would include its headers and the libWORLD.so. it could also be submitted to BREW to be available on the OS X package manager as well as libWORLD.dylib

[SeleDreams]

With this commit, project files are automatically generated for multiple IDEs with no difficulties including headers

and WORLD properly installs

[mmorise]

Thank you for your request. Since my main PC is Windows, I can't check the request with other OSs. But, it seems to be a useful modification, and I will accept this PR.

I leave the VS project files and the makefiles for the users having no cmake environment.