v0.3.0

Everything here was found by APPLYING the library to a real repository for
the first time, not by reading it. This is the release that justifies the
note at the top of this file about 1.0.0.

Added

• mkPackageFlake gains executable, which builds a delivered CLI from the
  preset's OWN resolved lispDerivation arguments. mkExecutable's args
  was documented as "the exact attrset you'd pass to lispDerivation", but the
  preset had already computed that attrset and exposed only the result — so a
  delivered binary re-spelled pname, lispSystem, meta, version and
  src in an escape hatch. Two sources of truth for the package's identity,
  inside the one function whose purpose is removing exactly that. The first
  package to deliver a CLI and carry lispDependencies would have shipped a
  binary silently missing them. The resolved attrset is also on the context
  for anything the argument does not cover; re-spelling args wholesale is
  rejected by name.
• mkExecutable gains installSource, plus a written contract for what
  $out contains and what a delivered image may assume about its
  surroundings. A Lisp image that resolves its ASDF source root from
  *runtime-pathname* found nothing, because this function published
  $out/bin and nothing else; the binary died on its first re-load of one of
  its own systems. Both sides were individually correct and disagreed
  silently, so the missing contract was the actual defect. The dependency
  closure is installed alongside the system's own tree — sources that are
  findable while their dependencies' are not fail at the same place, one
  asdf:load-system later.

Changed

• Breaking: mkPackageFlake's root is required. root ? self was the
  obvious default and never worked: a flake's self is an attrset carrying
  an outPath, and lib.fileset rejects it, so the failure surfaced from
  inside mkLispSource naming neither self nor the argument responsible.
  It survived the suite because examples are handed pkgs and cl directly
  and their self was already a path literal — the test suite could not
  reach the bug because it never exercises a real flake self.
• Delivered executables carry their version in the store path again.