v1.0.0

Initial release.

• Tagged-PDF (Section 508 / WCAG) support layered onto published prawn
  (~> 2.5) and pdf-core (~> 0.10) via prepend and additive re-opens —
  no forking.
• High-level document API on Prawn::Document: tagged?, structure,
  structure_container, artifact, heading, paragraph, figure, plus the
  marked: and language: document options.
• Structure attributes: :Alt, :ActualText, :Lang, :Scope.
• Low-level PDF::Core::MarkedContent (BMC/BDC/EMC) and
  PDF::Core::StructureTree (StructTreeRoot, structure elements, ParentTree,
  MCID allocation).
• Optional prawn-table (~> 0.2) tagging: <Table>/<TR>/<TH>/<TD>
  with header detection and /Scope. Activated automatically when
  prawn-table is present; not a required dependency.

Repackaged from the stalled upstream PRs prawnpdf/pdf-core#67,
prawnpdf/prawn#1391, and prawnpdf/prawn-table#164.