Improve error messages for parameter errors

I really don't know anything about ErrorBlock, so I haven't written a
description for that one.
Add name of attribute to ErrorAttributeMissing
Add mipmap generation
Merge pull request #263 from hannobraun/mesh-error

Add name of attribute to ErrorAttributeMissing
Merge pull request #264 from cmr/master

Add mipmap generation
Add a Blob implementation for slices
Merge pull request #265 from cmr/master

Add a Blob implementation for slices
fixed example for lastest vertex-rs
Merge pull request #262 from hannobraun/error-messages

Improve error messages for parameter errors
Merge pull request #267 from csherratt/master

fixed example for lastest vertex-rs
Moved PrimitiveType from Mesh into *Slice
#[packed] -> #[repr(packed)]
Merge pull request #272 from bjz/fix-tests

#[packed] -> #[repr(packed)]
Merge pull request #271 from sectopod/slice

Moved PrimitiveType from Mesh into *Slice
Remove Color type to make ClearData cleaner

We can't currently derive from fixed length arrays, but I think it's better to have an API that is consistent with our goals of mathematics library agnosticism.
Merge pull request #274 from bjz/remove-color-type

Remove Color type to make ClearData cleaner
Clean up examples

- Use rust-style field names for `#[shader_param]` and `#[vertex_format]` structs
- Pass the model, view, and projection matrices into the shaders separately
- Remove pointless setting of `.x.x` matrix element
- Clean up formatting
Combine model/view/proj matrices into single uniform for cube example
Merge pull request #273 from bjz/examples

Clean up examples
Update for api-change in upstream of vertex-rs.