A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
AFAIK there is no library, because the STL file format is not complicated:
http://www.fabbers.com/tech/STL_Format
As you see there are 2 formats: ASCII or binary, that's all.
But what do you want to do with the numbers you read from the file? Write into cells? And then?
If you need further help please upload your file on an online file hoster like www.dropbox.com and post the download link here.
Andreas.