DOC: some stylistic improvements to docstring rendering in documentation
DOC: correction of example in unstack docstring
DOC: warning about using numexpr > 2.1 as it has a backward incompatible change
     that affects PyTables < 3.0
BUG: Constrain date parsing from strings a little bit more #4601

Currently dateutil will parse almost any string into a datetime.  This
change adds a filter in front of dateutil that will prevent it from
parsing certain strings that don't look like datetimes:

1) Strings that parse to float values that are less than 1000
2) Certain special one character strings (this was already in there,
   this just moves that code)

Additionally, this filters out datetimes that are out of range for the
datetime64[ns] type.  Currently any out-of-range datetimes will just
overflow and be mapped to some random time within the bounds of
datetime64[ns].
Merge pull request #4776 from jorisvandenbossche/doc-unstack

DOC: correction of example in unstack docstring
Merge pull request #4901 from cpcloud/print-versions-without-pandas

CI: allow print_versions to work without pandas install
Merge pull request #4775 from jorisvandenbossche/docstring-rendering

DOC: some stylistic improvements to docstring rendering in documentation
Merge branch 'fix-float-into-datetime' of https://github.com/danbirken/pandas into danbirken-fix-float-into-datetime
CLN: just call print_versions via subprocess