[WIP] Use associated types for device resources

[brendanzab]

Gets us closer to #416.

An alternative to #517

For now I am hard coding the GlDevice as the buffer handle device parameters. Currently getting a lifetime error though:

src/device/lib.rs:203:9: 203:17 error: the associated type `<D as Device>::Buffer` may not live long enough [E0311]
src/device/lib.rs:203         self.raw.get_info()
                              ^~~~~~~~
src/device/lib.rs:203:9: 203:17 help: consider adding an explicit lifetime bound for `<D as Device>::Buffer`
src/device/lib.rs:203         self.raw.get_info()
                              ^~~~~~~~
src/device/lib.rs:202:43: 204:6 note: the associated type `<D as Device>::Buffer` must be valid for the anonymous lifetime #1 defined on the block at 202:42...
src/device/lib.rs:202     pub fn get_info(&self) -> &BufferInfo {
src/device/lib.rs:203         self.raw.get_info()
src/device/lib.rs:204     }
src/device/lib.rs:203:9: 203:17 note: ...so that the reference type `&Handle<<D as Device>::Buffer, BufferInfo>` does not outlive the data it points at
src/device/lib.rs:203         self.raw.get_info()
                              ^~~~~~~~
src/device/lib.rs:203:9: 203:17 error: the associated type `<D as Device>::Buffer` may not live long enough [E0311]
src/device/lib.rs:203         self.raw.get_info()
                              ^~~~~~~~
src/device/lib.rs:203:9: 203:17 help: consider adding an explicit lifetime bound for `<D as Device>::Buffer`
src/device/lib.rs:203         self.raw.get_info()
                              ^~~~~~~~
src/device/lib.rs:202:43: 204:6 note: the associated type `<D as Device>::Buffer` must be valid for the anonymous lifetime #1 defined on the block at 202:42...
src/device/lib.rs:202     pub fn get_info(&self) -> &BufferInfo {
src/device/lib.rs:203         self.raw.get_info()
src/device/lib.rs:204     }
src/device/lib.rs:203:9: 203:17 note: ...so that the reference type `&Handle<<D as Device>::Buffer, BufferInfo>` does not outlive the data it points at
src/device/lib.rs:203         self.raw.get_info()
                              ^~~~~~~~
error: aborting due to 2 previous errors
Could not compile `gfx_device_gl`.

[kvark]

Closing in favor of #564