Re-designed, code checked

Added: more than one cutoff for NDCG.
Added: two types of NDCG computations (linear and exponential)
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Quick fix for headerlines in CSV files
Merge pull request #30 from alansaid/master

Adding check for text headers in csv/tsv files