Extra annotation information for matches/offtargets

[vineetbansal]

One idea to attach extra annotation information for matches and offtargets would be to have guidescan enumerate take in an optional BED/GTF file and add selected/all columns from it to the output BED file.

samtools/bedtools may well already do this kind of merge, so it may not be technically needed (except for offtargets which will be tricky to handle).