Merge pull request #289 from sectopod/instance

Instancing
Use mask_write

Closes #148
Remove undefined behavior in offset computation

Closes #156
Merge pull request #291 from cmr/mask_write

Use mask_write
Merge pull request #292 from cmr/offset_of

Remove undefined behavior in offset computation
Fixed parameter allocations in the front-end
Merge pull request #295 from kvark/alloc

Fixed parameter allocations in the front-end
Removed support for instance rate from vertex_format macro. Added from_format_instanced() helper function to the Mesh