Allow the optional emission of sv length of evidence

[yfarjoun]

After calling sv's the vcf record include the median sv length found in the reads that support the SV in question. It is sometimes useful to know the various SV-lengths that went into a particular SV (for debugging purposes and for fine-tuning the parameters controling the clustering of evidence onto individual SVs, for example)

It would be nice to be able to (optionally) emit the individual lengths of the SV's as seen in the evidence (reads). This could be written to the VCF as a list of integers in a new tag (for example SVLENGTHS)

As I've already written the code to do this, I'll be submitting a PR shortly, however, I'm happy do discuss the merits of the idea here, and the details of the implementation on the PR.

Thanks!