Vcfio

sort headers when writing them to VcfWriter

add order headers when writing header to vcf file

What's Changed
* Merge changes from vcfio-internal-v0.1.8 by shencar in https://github.com/emedgene/vcfio/pull/6
* Enhancement | Remove VcfReader.get_value() by shencar in https://github.com/emedgene/vcfio/pull/7


**Full Changelog**: https://github.com/emedgene/vcfio/compare/1.1.0...1.1.1

**Full Changelog**: https://github.com/emedgene/vcfio/compare/1.1.0...1.1.1.dev2

remove get_value