v0.3.0

A language-mode release. A mode now carries the initial ISO flag values that go with its predefined
surface, not just the surface itself, and the new opt-in Modern mode starts double_quotes at
chars — so a double-quoted token reads as a list of one-character atoms, which is the convention
the newer Prolog systems settled on and what makes DCGs over text readable. Extended remains the
default and keeps the ISO initial value codes, so existing programs are unaffected.

Selecting a mode is now done by name everywhere, which replaces the 0.2.0 strict-ISO booleans.

Added

• A Modern language mode: the extended predefined surface with double_quotes seeded at chars.
  It is available from the embedding constructor, dotnet prolog, generated code, and .dplproj
  builds, and generated source still refuses to install into an engine created in a different mode.
• dotnet prolog run --mode extended|strict-iso|modern, and the DotPrologLanguageMode property
  for .dplproj projects. Mode names parse case-insensitively from one shared table, so the command
  line and MSBuild cannot drift apart.
• BytecodeProgram.InitialDoubleQuotes, recording the value the flag was seeded with before any
  source was read.
• A TextGrammar sample: a .dplproj application in Modern mode that decomposes a string, sums a
  run of numbers, and splits a sentence into words with DCGs written against characters.
• NativeAOT acceptance coverage for Modern mode, exercising build-time compiled clauses, the
  reader running inside the published binary, a consulted grammar, load-unit flag scope, and the
  mode-mismatch guard.
• Benchmarks comparing engine construction and consulting across language modes.

Changed

• double_quotes is scoped to the load unit. A set_prolog_flag(double_quotes, _) directive still
  governs the rest of the file that issued it, and the value in force when that file began is
  restored when it finishes, including when a directive throws. A library that declares its own
  convention can no longer change how whatever is consulted next is read. Deferred
  initialization/1 goals observe the restored value.
• The bundled bootstrap and standard libraries are read under codes in every mode; they are
  processor implementation, so a host's choice of dialect does not reinterpret them.
• A program's language mode is validated against an explicit allowlist, so a mode cannot be accepted
  before it has been given its initial flag values.

Removed

• dotnet prolog run --strict-iso, replaced by --mode strict-iso.
• The DotPrologStrictIso MSBuild property, replaced by DotPrologLanguageMode. A project setting
  the old property now fails the build rather than silently ignoring it.

Compatibility

• The initial double_quotes value stays codes in Extended and StrictIso, as ISO/IEC 13211-1
  requires. Modern is an extension and sits outside the conformance claim.
• Scoping double_quotes to the load unit changes an observable behavior that no previous release
  pinned. Source that relied on a directive outliving its file must set the flag in each file that
  needs it.