Parse Excel from in-memory file object
We came across a situation where we had a file object representing Excel data (came from HTTP POST but I'm thinking it could also come from MongoDB for example), and would've liked to pass it directly to Pandas to parse (vs saving it to disk and passing path to Pandas).

Could this be possible?

I saw that xlrd had `file_contents` as a possible argument of `open_workbook`:
https://github.com/python-excel/xlrd/blob/master/xlrd/__init__.py#L385

Maybe `ExcelFile` in Pandas could take `path_or_buffer` as argument, and pass along the correct one to xlrd.
https://github.com/pydata/pandas/blob/master/pandas/io/parsers.py#L1133

Don't know if that could work for openpyxl also.

Thoughts?

Thanks!
Nicolas
