Add support for breakends in VCF

[alumi]

Summary

This PR adds basic support for breakends in VCF.
Breakends are variant records which have SVTYPE=BND in the INFO field.
They have a dedicated format of string representation for ALT field.
For more details, please refer to the spec "5.4 Specifying complex rearrangements with breakends"

Tests

• lein check 🆗
• lein test :all 🆗
• lein cloverage 🆗

[codecov]

Codecov Report

Merging #163 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #163      +/-   ##
=========================================
+ Coverage   86.02%   86.1%   +0.08%     
=========================================
  Files          71      71              
  Lines        5387    5419      +32     
  Branches      489     489              
=========================================
+ Hits         4634    4666      +32     
  Misses        264     264              
  Partials      489     489

Impacted Files	Coverage Δ
src/cljam/io/vcf/util.clj	90.52% <100%> (+1.91%)	⬆️

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[alumi]

Resolved conflicts with #162

[r6eve]

Thank you for the breakends support.
I'm halfway through my review. I left a comment about regexp.

[athos]

Thank you for working on this improvement 👍 Basically, it looks good to me.
Added a couple of minor comments.

[r6eve]

LGTM!

[alumi]

Thanks!! 🎉