src/download_encode_eclip/merge_eclip.py: modification of merge_files function to remove the heading chr in the first bed column

src/download_encode_eclip/get_encode_clips.py: modifications to be hable to download  RIP-seq, iCLIP and RIP-chip experiments

src/download_encode_eclip/*.py: creation of a module used to download all the eclip data (on hg19) from Encode