MarkdownPDF 0.3.0

Changed

• Restructure the repository as a pure, git-resolvable SwiftPM package, mirroring
  the MathTypeset layout: Package.swift at the repo root, Sources/, and
  Tests/. A consumer can now depend on it with
  .package(url: ".../MarkdownPDF.git"). One package, multiple MarkdownPDF*
  targets: the MarkdownPDF library, the MarkdownPDFLinux and MarkdownPDFMac
  renderer entry points, MarkdownPDFResume, and the engine documentation, with
  the full MarkdownPDFTests and MarkdownPDFResumeTests suites kept in the
  package (they @testable-import the engine, so they cannot live in a consumer).

Removed

• The markdownpdf / resumepdf command-line executables and the Apps/ and
  Main.xcworkspace developer shell move to the separate MarkdownPDFCli repo,
  which consumes this package plus MathTypeset. The engine repo is now library-only.