Cjg/new json

[Cody-G]

This modifies the command file format as discussed in #40. Old scripts used to generate command files should still work with this new version. However if you have any old command files that you want to read with ImagineInterface, then they may not read correctly after we merge this.

In case users do need to read old command files they can checkout the newly-tagged "v0.1" release. I'll wait a day or two for user comments before I merge this.

[codecov-io]

Codecov Report

Merging #42 into master will decrease coverage by 0.09%.
The diff coverage is 88.88%.

@@            Coverage Diff            @@
##           master      #42     +/-   ##
=========================================
- Coverage   83.26%   83.16%   -0.1%     
=========================================
  Files          12       12             
  Lines         962      992     +30     
=========================================
+ Hits          801      825     +24     
- Misses        161      167      +6

Impacted Files	Coverage Δ
src/parse.jl	85.54% <100%> (-0.09%)	⬇️
src/validate_single.jl	98.9% <100%> (ø)	⬆️
src/write.jl	91.2% <87.5%> (-2.24%)	⬇️
src/sequence_analysis.jl	81.25% <0%> (-12.5%)	⬇️
src/metadata_constants.jl	83.33% <0%> (+0.98%)	⬆️

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[Cody-G]

I added a couple of fixes, will merge this tomorrow if I don't get any complaints.