0.5.0

The top level of specsolve now holds only what you call. What a call returns
is in specsolve.types, and what it raises is in specsolve.errors. Any other
name under specsolve. is internal. A spilled sweep now reads like one held in
memory. This release breaks imports, one class name, one attribute and one
method. Nothing on disk changed: archives, spills and saved results written by
0.4.0 read back.

Breaks:

• Model, Result, Sweep, ResultArchive and SweepArchive are imported
  from specsolve.types, and so are the rows they hold: Record,
  Provenance, Metrics, Diagnostics and ConstraintRow. Write
  sps.types.Result for sps.Result. specsolve.relational.parquet is
  removed.
• Every error and SpecsolveWarning is imported from specsolve.errors.
  Write sps.errors.DataError for sps.DataError.
• SolveArchive is now ResultArchive. What an archive holds is
  archive.result for one solve and archive.sweep for a sweep; .answer is
  removed.
• Model.evaluator is private. An archive and a sweep still evaluate an
  expression the file never named.

New:

• On a spilled or scanned sweep, primal, dual, evaluate, to_pandas,
  to_dataarray, to_dataset and save read the name they are asked for
  instead of refusing. sweep.scan(name) returns the same frame, not yet read.
• The reference has an internal glossary: the names the code uses for its own
  parts, for anyone reading src/.

The pull requests since 0.4.0:

• refactor(archive): Record, Metrics and Provenance are imported from specsolve.relational.answer_layout, which an archive's own layout nests (#1823)
• refactor(archive): an archive of one solve is a ResultArchive read through .result, and a sweep archive is read through .sweep (#1828)
• feat(sweep): a spilled or scanned sweep's readers read the name they are asked for instead of refusing (#1830)
• refactor(api): what a call returns is imported from specsolve.types, and what it raises from specsolve.errors (#1833)