DOC to_datetime warning about dayfirst strictness
TST: remove double call to yahoo finance
Merge pull request #4175 from hayd/datetime_dayfirst_warning

DOC to_datetime warning about dayfirst strictness
Merge pull request #4176 from cpcloud/remove-yahoo-test

TST: remove double call to yahoo finance
CLN: write the attributes in a HDFStore as strings

     These strings are converted to bytes, previously these were written as unicode
Merge pull request #4178 from jreback/hdf_3k

CLN: write the attributes in a HDFStore as strings
TST: raise when no data are found when trying to dld multiple symbols
Merge pull request #4184 from cpcloud/fix-network-tests

TST: raise when no data are found when trying to dld multiple symbols