Rebuild high level on top of LL

[Bastacyclop]

1 - Rebuild gfx_render

First, we need to rebuild gfx_render on top of the new low level core.
It will incorporate the old features from gfx_core and gfx_render:

• Resource handles
• Mapping tracking
• Factory and Device, with the new terminology Device and Queue
• Encoder will not be Send anymore and rely on pools
• Slice, see #1392
• Pipeline mecanisms, see #1429

2 - Split gfx_app

Then, we want our crates to have clearer identities as discussed in gitter. That's why the old gfx_app will be split into three components:

• Utility code for the examples will live in the examples directory
• Utility code for the user will be moved into gfx_render (backend-agnostic)
• Backend selection will be the responsibility of a new gfx_frontend crate

3 - Improve

After these two steps, we will probably have a lot of polishing to do!

[msiglreith]

Thanks for taking a stab at this topic!
The mentioned points sound good so far.

Relevant discussion (but also partially outdated): #1281

[Bastacyclop]

Things to do after the first render implementation:

• Apply the conclusions of this Format discussion.
• Clean it up and handle errors
• Write the documentation

[kvark]

This is somewhat addressed by Rendy now
cc @omni-viral

[omni-viral]

Rendy doesn't have all necessary tools. Yet it already can do many things that good ol' gfx does for you.
As rendy is going to replace gfx in amethyst it ultimately will get all tools one needs.