ENH: Excel to support reading Timedeltas
ExcelFile should print out line or even cell warnings

Today I was spending quite some time debugging why a decoding error stopped the code from reading in a table.

I thought the skiprows counts from 0 (= Excel row 1). It was always failing.

In one line there were column headers, the next line contained units which couldn't probably be parsed.

I think it could be helpful if the parser would show the line number or even cell were it fails to ready (like due to decoding errors).
