TST/ERR: raise a ValueError at runtime for incompatible versions of openpyxl

instead of warning at import time

add openpyxl 2.0.3 to trigger travis fails on import
Merge pull request #7285 from cpcloud/openpyxl-format-string-fix-7284

BUG/CI/TST: fix format strings
BUG: BoolBlock shouldn't replace truthy values
ENH/TST: add anonymous reading of s3 for public buckets
Merge pull request #7304 from cpcloud/fix-replace-bool-yet-again-7140

BUG: replace() alters unrelated values
BUG/TST: should skip openpyxl before testing version compat
Merge pull request #7281 from cpcloud/public-s3-7246

ENH/TST: add anonymous reading of s3 for public buckets
Merge pull request #7311 from cpcloud/openpyxl-format-string-fix-7284

BUG/TST: should skip openpyxl before testing version compat
BUG: single group series should preserve group name
Merge pull request #7313 from cpcloud/fix-single-group-extract

BUG: single group series should preserve group name
BUG: do not check that val != val and not equal inf/-inf since by def val not eq val is nan
Merge pull request #7315 from cpcloud/fix-dropna-with-inf-7314

BUG: isnull doesn't properly check for inf when requested
CLN/DOC: Remove trailing whitespace from .rst files in doc folder
Merge pull request #7317 from bwignall/doc-trailingws

CLN/DOC: Remove trailing whitespace from .rst files in doc folder
BUG: inferred_freq results in None for eastern hemispheres timezones