Pre-0.8 audit

[joshlf]

• Audit top-level crate docs
• Audit top-level traits
  • KnownLayout
  • Immutable
  • Unaligned
  • TryFromBytes
  • FromZeros
  • FromBytes
  • IntoBytes
• Audit byte_slice module docs and traits: [byte_slice] Clean up docs and methods #1700
  • ByteSlice
  • ByteSliceMut
  • CloneableByteSlice
  • CopyableByteSlice
  • IntoByteSlice
  • IntoByteSliceMut
  • SplitByteSlice
  • SplitByteSliceMut
• Audit Ref module docs and type: [Ref] Clean up docs #1706
  • Ref methods which PME for ZST DSTs should document this behavior
  • Ref should document its intended use cases
• Audit macros
  • transmute!
  • transmute_ref!
  • transmute_mut!
  • try_transmute!
  • try_transmute_ref!
  • try_transmute_mut!
  • include_value!
• Audit byteorder module: [byteorder] Clean up docs #1707
  • seal ByteOrder trait: Seal ByteOrder trait #1698
• Audit error module: Implement TryReadFrom::map_src #1704
• Audit Unalign: [Unalign] Update docs #1701