Destructors are not run when calling `exit`

[paulthomson]

We should probably avoid calling exit and instead throw an exception, catch it in main and then exit. This allows destructors to execute. This may be important because helpful error messages may be hidden by unhelpful error messages about "leaking" objects. See mc-imperial/get-image-egl@063eb3b

We should also include the above commit!

[hevrard]

Sounds good!
It may be a bit more subtle here as the EGL / GLFW contexts are as isolated as possible in their own module.