0.7.0

• Add AttachmentLoader for creating region attachments
• Upstream fixes
  • Reduce allocations (EsotericSoftware/spine-runtimes#2325)
  • Fix double free of sequences in mesh attachments (EsotericSoftware/spine-runtimes#2394)
  • Fix buffer overflow when loading sequences with less than 10 frames (EsotericSoftware/spine-runtimes#2397)
  • Fix incorrect allocation of TransformTimeline (EsotericSoftware/spine-runtimes#2401)
• Remove unnecessary feature use_libc, use libc instead
• More clippy fixes
• Fixes for pointer, abi, and memory undefined behavior
• Lots of docs
• Return values now optional:
  • SkeletonData::audio_path
  • SkeletonData::images_path
  • SkeletonData::version
  • SlotData::attachment_name
  • SlotData::blend_mode
  • SlotData::color
  • TrackEntry::mixing_from
  • TrackEntry::mixing_to
  • TrackEntry::next
  • TrackEntry::previous
• Remove unnecessary functions:
  • Atlas::find_page_mut
  • Atlas::find_region_mut
  • Atlas::pages_mut
  • Atlas::regions_mut
  • AtlasPage::atlas_mut
  • AtlasRegion::page_mut
  • BoneData::color_mut
  • BoneData::parent_mut
  • BoneData::set_length
  • BoneData::set_position
  • BoneData::set_rotation
  • BoneData::set_scale_x
  • BoneData::set_scale_y
  • BoneData::set_scale
  • BoneData::set_shear_x
  • BoneData::set_shear_y
  • BoneData::set_shear
  • BoneData::set_skin_required
  • BoneData::set_transform_mode
  • BoneData::set_x
  • BoneData::set_y
  • SkeletonData::animation_at_index_mut
  • SkeletonData::animations_mut
  • SkeletonData::bone_at_index_mut
  • SkeletonData::bones_mut
  • SkeletonData::default_skin_mut
  • SkeletonData::find_animation_mut
  • SkeletonData::find_bone_mut
  • SkeletonData::find_skin_mut
  • SkeletonData::find_slot_mut
  • SkeletonData::skin_at_index_mut
  • SkeletonData::skins_mut
  • SkeletonData::slot_at_index_mut
  • SkeletonData::slots_mut
  • SlotData::bone_data_mut
  • TrackEntry::set_animation_time
  • TrackEntry::set_mixing_from
  • TrackEntry::set_mixing_to
  • TrackEntry::set_next
  • TrackEntry::set_previous
• Remove unnecessary types:
  • AtlasPageMutIterator
  • AtlasRegionMutIterator