DOC: note about query strings in HDFStore selection
Merge pull request #6905 from cpcloud/query-doc

DOC: note about query strings in HDFStore selection
API: update SQL functional api #6300
TST: test new read_sql api
Merge pull request #6867 from jorisvandenbossche/sql-api

API: update SQL functional api (GH6300)
BUG/ENH: Warn when falling back to python parser

-Warn when falling back to python parser due to C-unsupported options
(via new class, ParserWarning).
-Copy tests that previously fell back to python from ParserTests to
TestPythonParser and assert that they produce ParserWarnings when run
under other engines.
-Fix C parser handling of leading whitespace and \r-delimited files
(add test)
-Translate sep='\s+' to delim_whitespace=True (add test)
-Specify engine='python' in tests with C-unsupported options to avoid
warnings
-Specify engine='python' in tests with sep='\s+' and `MultiIndex`ed
input (avoids error; C engine doesn't support multiple indexes)