support type aliases

[npmccallum]

rust-lang/rust#10374

Because of that bug, we can't really use enumflags when we need to serialize to an architecture dependent size. For example: std::os::raw::c_ulong. We can either try to get it fixed in the compiler or we can try to work around it.

[MaikKlein]

I am a bit confused, you don't serialize the enum you serialize the bitflag struct https://docs.rs/enumflags/0.3.0/enumflags/struct.BitFlags.html and enumflags only supports a few basic types so far https://docs.rs/enumflags/0.3.0/enumflags/trait.BitFlagNum.html.

Also the BitFlags struct is not repr(C) yet. I also wanted to have something like type aliases in ash. I also should add support for serde in the future. But I am currently very busy, I am not sure when I will find some time to implement all of this.