BUG: use the "join" string in Appender decorator

The docstring for Appender decorator says that "join" parameter is used to join the docstring and addendum.  This commit brings the code in line with the documentation.
VBENCH: rename parser.py to parser_vb.py
BUG: fix broken df.info() test_info_duplicate_columns
DOC: add a couple plt.close('all') to avoid warning
DOC: fix warning + some stylistic corrections
Modified test_pow function in computation/tests/test_eval.py to use assert_allclose rather than assert_all_equal to avoid machine precision failures in TestEvalNumexprPandas/Numpy.  Fixes issue #5981.
Merge pull request #5979 from y-p/PR_VB_parser_rename

VBENCH: rename parser.py to parser_vb.py
Merge pull request #5980 from jorisvandenbossche/doc-plot-warning

DOC: add a couple plt.close('all') to avoid warning
DOC: correction of docstring dtypes/ftypes
Merge pull request #5982 from drudd/master

Modified test_pow function in computation/tests/test_eval.py to use asse...
Merge pull request #5984 from jorisvandenbossche/doc-dtypes

DOC: correction of docstring dtypes/ftypes
API: Panel.dtypes to use generic method; add tests for Panel4D for same

DOC: updated api docs for panel/panel4d
DOC: in ReST, a sublabel defines it's parent. latex complains of dupe
Merge pull request #5985 from y-p/PR_doc_latex_fix

DOC: in ReST, a sublabel defines it's parent. latex complains of dupe
Merge pull request #5983 from jreback/panel_dtypes

API: Panel.dtypes to use generic method; add tests for Panel4D for same
DOC: add 0.13.1 whatsnew to the index
DOC: tutorials
DOC: whitespace fixes for tutorials update GH5929
Change "methdo" to "method" in asfreq's docstring.
Merge pull request #5989 from  adeodatus/master

* adeodatus-master:
  Change "methdo" to "method" in asfreq's docstring.