fix loss of data
fix loss of data

Data loss is caused by the fact that expat can perform multiple call to handleCharData() for the same cell value.
More explanation can be found here : https://docs.python.org/3/library/pyexpat.html#xml.parsers.expat.xmlparser.buffer_text
This could lead to more memory consumption for very big cell but it should not be the common case.
Else, the code should be rewritten to handle multiple call of handleCharData() for the same cell value.
This is supposed to fix issue #142 "Digits lost in conversion".
dilshod/xlsx2csv