The class is now created always on the stack, so the user doesn't have
to delete it explicitly. It's now possible to write less verbose
shader code, instead of three lines before:
Shader* s = Shader::fromFile(Shader::Fragment, "Shader.frag");
attachShader(s);
// ...
delete s;
It's now only one:
attachShader(Shader::fromFile(Shader::Fragment, "Shader.frag"));
Removed another old overdone code, the attributes are now bound
directly, without saving the data to some temporary location and then
binding everything at once in link().