Fix inline context padding on inline-block.

Fixes categories bar on wikipedia - ref #2554.
Rename macros crate to plugins
Add license headers
Fix CEF
Merge pull request #3435 from Manishearth/macro_reorg

Reorganize macros crate; r=jdm
Merge pull request #3460 from glennw/inline-block-padding

Fix inline context padding on inline-block.
Disable non_snake_case warnings in devtools
Fix other warnings in devtools
Avoid an unnecessary string allocation in allow_cross_origin_request.
Merge pull request #3461 from mbrubeck/warnings

Fix misc warnings in devtools crates. r=jdm
Merge pull request #3462 from Ms2ger/as-slice

Avoid an unnecessary string allocation in allow_cross_origin_request; r=jdm