Add EGL 1.5 support, bug fix and refactoring.

[timothee-haudebourg]

So I have added support for EGL 1.5. To do so I first had to refactor the code and order everything by EGL version so I can find my way around (sorry about that). I think it will be more sustainable this way, since it follows the structure of the original egl.h file it should be easier for other people to understand the structure of lib.rs.

On the way i've spotted a bug: the eglGetConfigs function was wrongly typed. configs
should be a pointer to an array of EGLConfig, hence have type *mut EGLConfig where it had the (wrong) type EGLConfig. Note that, if I fixed the signature problem, the bug is still here:

pub fn get_configs(display: EGLDisplay, config_size: EGLint) -> EGLConfigList {
    unsafe {
        let list = EGLConfigList{ configs: ptr::null_mut(),
                                  count:   0 };

        ffi::eglGetConfigs(display, list.configs, config_size, list.count as *mut int32_t);

        list
    }
}

You are always calling eglGetConfigs with the null pointer. According to the Khronos documentation,

configs does not return values, if it is specified as NULL

So you'r outputting a EGLConfigList instance where configs is always null (ouch).

[timothee-haudebourg]

I've added a proposition to fix the get_configs issue. Now the function outputs a Vec<EGLConfig>.