Version 1.5.4 release

• Using the versioned www.gstatic.com WASM and Javascript decoders continues
  to be recommended. To use v1.5.4, use this URL:
  • https://www.gstatic.com/draco/versioned/decoders/1.5.4/*
• Added partial support for glTF extensions EXT_mesh_features and
  EXT_structural_metadata.
• Bug fixes.
• Security fixes.