Perform a left_bind operation on a GRanges list, appending scores to mcols.
     
    
    Usage
    .granges_left_join(grlist, labels, granges = NULL)
 
    
    Arguments
- grlist
- A list of GRanges objects that have all the same fields. 
- labels
- Vector of names for the score columns. 
- granges
- Optional granges with name field on it 
 
    
    Value
    A Sorted GRanges object with all the columns.
     
    
    Details
    This assumes that you are trying to join things that match (bins generated
from the same parameters, BED intersections from the same BED.)