added the ability to pull links from excel cells
added ability for links in xlsx files
performance fix for huge xlsx files with links.

Removed the path attribute lookup and cached the rels before the hyperlink loop
checking for nil rels. oops.
issue # 73 - Roo::Spreadsheet.open extension with a dot. - fixed
Fixes remote CSV filename from getting set to 'nil'.
Support sheets in Base#to_matrix
Add :mode option, passed to Spreadsheet.open
Merge pull request #88 from blambeau/master

Add :mode option, passed to Spreadsheet.open
Merge pull request #76 from neerajkumar/issues

issue # 73 - Roo::Spreadsheet.open extension with a dot. - fixed
Merge pull request #77 from CIRCUITLLC/remote_csv

Fixes remote CSV filename from getting set to 'nil'.
Merge pull request #87 from jonah-carbonfive/bugs/to-matrix-using-sheets

Support sheets in Base#to_matrix
Merge pull request #51 from dizer/master

open remote paths
Add a test for #51
Merge pull request #47 from toreym/excel_links

added the ability to pull links from excel cells