Made toIntervalList an iterator as well ...

[yfarjoun]

So that large VCFs can be turned into intervalLists by operating on them in a stream rather than loading all the intervals into memory.

Description

Please explain the changes you made here. Explain the motivation for making this change. What existing problem does the pull request solve?

Things to think about before submitting:

• [ ] Make sure your changes compile and new tests pass locally.
• [ ] Add new tests or update existing ones:
  • A bug fix should include a test that previously would have failed and passes now.
  • New features should come with new tests that exercise and validate the new functionality.
• [ ] Extended the README / documentation, if necessary
• [ ] Check your code style.
• [ ] Write a clear commit title and message
  • The commit message should describe what changed and is targeted at htsjdk developers
  • Breaking changes should be mentioned in the commit message.

[codecov-io]

Codecov Report

Merging #1455 into master will increase coverage by 0.019%. The diff coverage is 91.176%.

@@              Coverage Diff               @@
##             master     #1455       +/-   ##
==============================================
+ Coverage     68.41%   68.429%   +0.019%     
- Complexity     8499      8505        +6     
==============================================
  Files           583       584        +1     
  Lines         34413     34478       +65     
  Branches       5729      5730        +1     
==============================================
+ Hits          23542     23593       +51     
- Misses         8650      8665       +15     
+ Partials       2221      2220        -1

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/htsjdk/tribble/MutableFeature.java	100% <100%> (ø)	6 <6> (?)
...c/main/java/htsjdk/samtools/util/IntervalList.java	73.333% <86.842%> (+1.153%)	59 <0> (-5)	:arrow_down:
...rc/main/java/htsjdk/variant/vcf/VCFFileReader.java	66.667% <93.75%> (-0.498%)	30 <6> (+8)
src/main/java/htsjdk/samtools/util/Interval.java	66.667% <0%> (-1.667%)	26% <0%> (-3%)

[yfarjoun]

Thanks for the review @lbergelson. back to you.