Create negative set from the peak call file

[Mamie]

• Input: intervals of peak call regions
• Output: sliding window intervals of the regions outside the intervals covered by the called peak

[Mamie]

Updates:
The negative regions should be from the complement of the union of H3K4me3 and H3K27Ac peak regions.
No sliding window for now. The negative set is selected as the flanking region outside the 1kb on each side of each peak. If there is less negative than positive, run sliding window. The final output should be all 2 kb intervals.