Add VCF 4.3 writing support

[andersleung]

• Percent encoding of special characters is now supported in VCFWriter
• Default behavior is to write VCFs as latest guaranteed compatible version (pre v4.3 -> 4.2 and v4.3 -> v4.3), but system property can be set to automatically attempt conversion from v4.2 -> v4.3 and fall back to v4.2 if conversion is impossible, or alternatively fail with error if conversion is impossible
• Fix bug where extra fields in INFO and FORMAT header lines are dropped

@lbergelson

Description

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

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• [ ] Extended the README / documentation, if necessary
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[lbergelson]

@cmnbroad This PR is relevant to the headerline refactor.

[cmnbroad]

@andersleung I won't have time to review this until next week, but I took a quick look and one suggestion would be to integrate VCFPercentEncoder and it's tests into the existing VCFPercentEncodedTextTransformer and test classes. The VCFTextTransformer interface will have to be extended to have encode methods to do this, but since the encoder and decoder are complementary, the code, and tests, should live together. Also then the test cases won't have to be duplicated, and the tests can use composition to verify that encode and decode are inverses, i.e., decode(encode(a)) == a.