[bashtage]

…nd asset pricing

Docstrings only. With the docstrings removed, the code is identical to the base.

The three docstring sweeps of the areas were done independently and left the
documentation of the options with fixed values in different layouts. This makes
them one set.

Options with fixed values

• Short lists stay in the type line with braces, {"a", "b"}, with plain quoted
  values. Long lists, where the brace line would be longer than the 99 columns
  of flake8, use "str, optional" and list every accepted name, aliases included,
  in the description as bullets. A name comes first, then its aliases, in the
  same order everywhere: the kernels are "bartlett", "newey-west"; "parzen",
  "gallant"; "qs", "quadratic-spectral", "andrews".
• The lists of the kernels, of cov_type and of weight_type now have one layout
  in iv, panel, system and asset_pricing. Lists that were in Notes
  (KernelWeightMatrix, DriscollKraay, ACCovariance) or in prose (the panel fit
  methods, FamaMacBeth, the Kleibergen-Paap functions) are in the description of
  the parameter. FamaMacBeth.fit and the asset pricing fit methods use braces,
  because their lists fit on a line.
• Every option is shown in lower case, including the names of the classes that
  cov_type accepts ("homoskedasticcovariance", "kernelcovariance", ...).
• Each option with named values says "The names are not case sensitive.": cov_type,
  weight_type, kernel, method, group and precision, and the kernel of the
  cov_config and weight_config. dummy_matrix is case sensitive and does not.
  Every name in the lists was checked against the code, in lower, upper and title case.

extra_df

• The fit of IV2SLS and IVLIML accepts the key extra_df in cov_config and passes
  it to the covariance estimator, which scales by n / (n - k - extra_df) if
  debiased is True. It is documented now.
• AbsorbingLS.fit accepts it too, but replaces it with the number of absorbed
  effects if debiased is True and does not use it otherwise, so it is not
  documented as an option there.

Raises

• The ten fit methods that had a second ValueError entry for a key of cov_config
  that the covariance estimator does not accept (IV2SLS and IVLIML, IVGMM,
  IVGMMCUE, IVJIVE, AbsorbingLS, SUR and IV3SLS, IVSystemGMM, TradedFactorModel,
  LinearFactorModel and LinearFactorModelGMM) have one ValueError entry that
  lists all the conditions, as the panel fit methods do.