Handle multiple motifs for same TF.

[j-andrews7]

Some motif databases have multiples motifs for the same transcription factor. Would like to check both motifs, but need a way to differentiate the two. An easy solution would be to just tack on a suffix in the motif database file when calculating thresholds.

For example:

124 AIRE
16 12 14 0 0 1 9
7 8 9 1 0 7 16
1 2 5 0 0 9 22
4 5 11 36 37 26 1

125 AIRE
counts

Would become:

124 AIRE
counts

125 AIRE.2
counts

Or something along those lines.

[j-andrews7]

This has been addressed for tf_expression.py at least, see #32. Merged into #33.