make_grid: make grid for enrichment scan.
In jnkoberstein/DEScan: Differential Enrichment Scan

make grid for enrichment scan.

1 2	make_grid(bed, fraglen, rlen, min_bin = 10, min_rds = 0, grid_st = NA, grid_ed = NA)

`fraglen`	Integer indicating the average DNA fragment length in bp
`rlen`	Integer indicating the read length in bp
`path`	Path to alignement files.
`chr`	Integer specifying which chromosme to limit analysis to.
`min_win`	Integer indicating the minimum window size to be used in constructing grid
`max_win`	Integer indicating the maximum window size to be used in constructing grid
`blocksize`	Integer indicating how large of a chunk of the chromosome will be analyzed at a time