Remove the special case for empty dataframes in to_html.

Fixes issue #6062.
API: default value for read_excel sheet (GH6573)
FIX str.match uses na flag
TST: enable MySQL tests
ENH/TST: Support for non-ascii encodings in DataFrame.to_excel (GH3710)
Merge branch 'excel_default' of https://github.com/clarkfitzg/pandas into clarkfitzg-excel_default
Merge pull request #6613 from jorisvandenbossche/sql-mysql2

TST: enable MySQL tests
CLN #6589 remove print statements when sep=None is passed to read_csv

Simply removed unneceesary print.
Merge pull request #6615 from mangecoeur/CLN-6589

CLN #6589 remove print statements when sep=None is passed to read_csv
BUG/CLN: fix iloc when positional indexer matched Int64Index keys

Also, drop takeable parameter from reindex(...) function family.
BLD: add 3.4 build requirements and wheels
Merge pull request #6614 from immerrr/drop-reindex-takeable-param

BUG/CLN: fix iloc when positional indexer matched Int64Index key
ENH: Allow longtable in to_latex. Closes #6616.

DOC: Make note about booktabs package.

DOC: Add longtable to release notes.
BUG: Bug in fillna with limit and value specified
Merge pull request #6628 from jreback/fillna_limit

BUG: Bug in fillna with limit and value specified
BUG/API: allow TimeGrouper with other columns in a groupby (GH3794)
CLN/API: replace groupby.CustomGrouper with Grouper
         rename internally Grouper to BaseGrouper to avoid conflict
         TimeGrouper to now inherit from Grouper
DOC: update groupby docs for using pd.Grouper
BUG: Error in to_stata when DataFrame contains non-string column names

to_stata does not work correctly when used with non-string names.  Since
Stata requires string names, the proposed fix attempts to rename columns using
the string representation of the column name used.  The main method that
reformats column names was refactored to handle this case.

Patch includes additional fixes for detecting invalid names.

Patch includes some minor documentation fixes.
Merge pull request #6622 from bashtage/stata-timestamps

BUG: Error in to_stata when DataFrame contains non-string column names