Support for Excel Files in MHT (aka MHTML) Format
Some Excel Files are stored in MHT / MHTML / Single File Web Page/ Web Archive files.

Currently Pandas cannot handle these files, but rather produce:

```
XLRDError: Unsupported format, or corrupt file: Expected BOF record; found '\xef\xbb\xbfMIME-'
```

For example see: http://www.sec.gov/Archives/edgar/data/1490281/000149028113000033/Financial_Report.xls

I wonder if something like https://github.com/Modified/MHTifier can be used to exctract the content before passing to the xlrd library.
