code, tests & examples for (i) converting XML <-> JSON, & (ii) residuals

[matthewjohnpayne]

The changes in this branch are to perform the following

(1) allow conversion between XML <-> JSON files.

• The purpose is for my own convenience elsewhere in some other MPC development tasks, and is not specifically intended to be used to allow users to submit data in JSON format. It does however open the possibility of allowing that in the future.
• As per the extant XML <-> PSV conversion routines, these new XML <-> JSON routines are pure conversion routines: they do NOT perform any validation on the XML or JSON, nor do they require that the input be valid.

(2) provide examples (and validation tests) of ADES files that include RESIDUALS.

• It was not clear to me what the hell the allowed format was supposed to be, nor that there are two allowed variations-on-a-theme (one inside \<optical>, the other 'standalone'). As such I have made a couple of example data files (new_tests/input/*Residual.xml) , and provided some quick validation tests (new_tests/test_validationResiduals.py) to reassure myself that they work.

[matthewjohnpayne]

@federicaspoto : Thanks for looking at this.

• I added tests that import the json2xml & xml2json routines and call them as functions (in addition to the extant command-line call tests).
• I also improved all of the tests such that pytest can be called from anywhere (as previously written, I'd inadvertently required that the user run the tests from within new_tests)

With regards to your comment/questions regarding the format of input/*Residual.xml:

• The parts that looks like \<!-- ***** -- \> are the standard way to add comments to XML files.
• I'm primarily using them here as a means to highlight to my future-self that certain of the fields in the sample input residuals are optional (while the rest are required by the ADES schema).

[federicaspoto]

@matthewjohnpayne thank you! About my comment on the formatting, it was about the fields themselves, not the comments. But it is not important. It just looked weird on my screen.

[matthewjohnpayne]

@federicaspoto : no worries. I'm going to leave this open and let @stevechesley have a chance to look at it before I merge anything.

[matthewjohnpayne]

@stevechesley : thanks for adding in the shebangs. I added the pyyaml and xmltodict to the requirements file. I renamed the code to be 'xmltojson', etc For what it's worth, I also added in the future stuff, although I've no idea if there's any value to it anymore. All my tests still pass, so I'm going to go ahead and merge.