TST/DOC/BUG: Accommodate OpenPyXL incompatibility

*   Detect whether a compatible version is installed
*   Skip openpyxl unit tests instead of failing
*   Inhibit registration of `openpyxl` engine in `ExcelWriter`
*   Raise `UserWarning`
*   Document limitation as a known issue
*   Resolve issue #7169
Merge pull request #7214 from neirbowj/openpyxl_compat

TST/DOC: Test for and document incompatibility with openpyxl 2.0.0 and later
BUG: boxplot returns incorrect dict
DOC: corrections in v0.14.0
BUG: multi-index output formatting
Merge pull request #7232 from bjonen/fix_7174

BUG: multi-index output formatting is buggy (GH7174)
DOC: fix api docs
DOC: clean-up docstrings of option functions

so they render nice with sphinx without warnings
Merge pull request #7236 from jorisvandenbossche/doc-fixes2

DOC: clean-up docstrings of option functions
DOC: corrections in v0.14.0 / release
DOC: put in anticipated release date in release / v0.14.0 (May 31, 2014)
TST/CLN: remove prints (esp of unicode), replacing with com.pprint_thing (GH7247)
Merge pull request #7248 from jreback/fix_print

TST/CLN: remove prints (esp of unicode), replacing with com.pprint_thing (GH7247)
Merge pull request #7225 from sinhrks/boxbug

BUG: boxplot returns incorrect dict
API: let +, * and - pass thru but eval via Python

But give a warning suggesting a better way to do it
Merge pull request #7245 from cpcloud/bool-warn-and-work-7210

WRN: let + * and - pass thru on boolean with a warning