0.4.0

An archive now says what produced it, and a directory of archives reads as one
table per file. This release breaks archives, spills and saved results from
0.3.0, a model file that uses a reserved name, one import and one keyword.

Breaks:

• An archive, a sweep spill or a saved result written by 0.3.0 is refused by
  name. Its format.json names the specsolve that wrote it: read it with that
  release.
• A spec that declares a name starting with specsolve_, in any letter case,
  is refused. Rename the name. The prefix is reserved for the columns
  specsolve adds.
• The readers of a sweep return the answer. An EachWindow sweep comes back
  over the model's own coordinates, and the lookahead rows are dropped.
  original_index= is removed. To get the frames of each window, pass
  per_window=True.
• A sweep archive holds the answer. To archive the frames of each window too,
  pass keep_windows=True to solve_over.
• SliceMetrics is removed. A row of sweep.metrics is a Metrics row, and
  loaded is now loads, which is 0 or 1.
• The run column of record and metrics is now specsolve_run.

New:

• Every table in an archive carries specsolve_run, the archive's own name.
  record.parquet and metrics.parquet have the same columns for a solve and
  for every kind of sweep. A sweep names each slice in slice_axis and
  slice.
• catalog.parquet lists each file an archive holds, with its kind,
  description and dimensions.
• An archive holds each source as the tidy table that the solve read.
  sps.tidy(spec, sources) returns those tables.
• The record names the solver, its version, its options, and the specsolve
  and mathspec versions. The options are a JSON string. To record more
  options than the solver's list, pass record_options=.
• specsolve requires mathspec>=0.2.1,<0.3, so a release installed later
  gets the mathspec it was released with.

Fixes:

• A sweep key named like a metrics column, such as loads, is refused before a
  slice is solved.
• A sweep over an index given as an iterator reads it once, and every slice
  and the archive see the same labels.

The pull requests since 0.3.0:

• fix(deps): an installed specsolve release keeps the mathspec minor version it was released against (#1816)
• feat(archive): every archived table carries the run it came from as specsolve_run, and names starting with specsolve_ are reserved (#1809)
• feat(archive): an archive's record and metrics have the same columns for a solve and for every kind of sweep (#1810)
• feat(archive): an archive lists every name it holds, its kind, description and dimensions in catalog.parquet (#1812)
• feat(sweep): a sweep reads and archives its answer over the model's own coordinates by default, and keeps the per-window frames only on request (#1811)
• feat(data): an archive holds each source as the tidy table the solve read, and tidy() returns those tables (#1813)
• fix(sweep): a sweep key named like a metrics column is refused before a slice is solved (#1820)
• feat(archive): an archived answer names the solver, its options and the specsolve and mathspec versions that produced it (#1817)
• feat(api): a caller can name more solver options whose value the record keeps (#1818)