5.4.0: RFC 336

• Implemented second step for #86: Add an E_DEPRECATED warning to the
  hacklang annotation syntax <<...>>; details in xp-framework/ast#9
  (@thekid)
• Merged PR #89: Add annotation type mappings to TARGET_ANNO detail
  (@thekid)
• Changed PHP 8 attributes to be emitted in XP meta information without
  namespaces, and with their first characters lowercased. This way, code
  using annotations will continue to work, see xp-framework/rfc#336.
  (@thekid)