Use [dev_dependencies.*] to reduce excessive recompilation

See rust-lang/cargo#523

Still doesn't solve the multiple recompilations during `make test` though.
Fix warnings
Add missing copyright headers to source files and READMEs
Merge pull request #366 from bjz/warnings

Fix warnings
Merge pull request #367 from bjz/copyright-headers

Add missing copyright headers to source files and READMEs
Merge pull request #365 from bjz/examples

Use [dev_dependencies.*] to reduce excessive recompilation
Make OwnerBatch::param public

Closes https://github.com/gfx-rs/gfx-rs/issues/368
Merge pull request #369 from bvssvni/pub-param

Make OwnerBatch::param public
Derived PartialEq for shader Stage
Merge pull request #370 from sectopod/master

Derived PartialEq for shader Stage
Check for errors after every draw command
Print more useful information on errors

The "if cfg!(not(ndebug))" mirrors the implementation of
debug_assert_eq!, so it shouldn't be any more expensive than the macro
itself.
Merge pull request #373 from hannobraun/error-checking

Improve error checking
Rename ErrorType to GlError

GlError is more specific and sounds nicer to me.
Simplify GlDevice::get_error
Move creation code for GlError out of GlContext

This makes GlError useful outside of GlContext.
Merge pull request #374 from hannobraun/gl-error-handling

Improve handling of OpenGL errors
Fix stack overflow when formatting ColorMask

The old implementation of ColorMask relied on itself for formatting,
leading to an infinite recursive loop and eventual stack overflow.

Thanks to @bjz for suggesting this approach.
Return TextureError, if TextureInfo is invalid
Improve error messages for TextureError