* Fixed the build for web using CMake.

I found that the build for me was failing and I added some if defined checks in the core.c file where the glfwSetWindowAttrib was used. (error: implicit declaration of function 'glfwSetWindowAttrib' is invalid in C99 [-Werror,-Wimplicit-function-declaration])

I also changed some values in the toolchain file so that it correctly uses the .bat files when on windows.

* Cleaned up the additional variables (they are not important)

* Added more improvements to cmakelists

Added the option to use the system provided Emscripten toolchain to be more uniform with other libraries.

Fixed and issue which prevented example being built from cmake and also building with html extensions properly.

* Fixed ENUM to STRING because of a missed warning

Did this ever work? Surely, doesn't look like it...