add configuration for xsi:nil="true" conversion to null

[meiskalt7]

Hello :-)

I add configuration for xsi:nil="true" conversion to null. In JSON spec null should be represented like
{ key: null }
link: https://stackoverflow.com/questions/21120999/representing-null-in-json

Please check it and merge, cause it is necessary for many dependent projects.

What problem does this code solve?
Representation of null in accordance with JSON spec

Risks
Low

Changes to the API?
No, only addition new constructor for XMLParserConfiguration

Will this require a new release?
Yes.

Should the documentation be updated?
Yes. Javadoc already updated.

Does it break the unit tests?
No

Was any code refactored in this commit?
Yes, changes were made to the number parsing methods for XML and added new configuration
(no changes in public methods)

Backward compatibility
Yes

Review status
APPROVED

[stleary]

HI @meiskalt7. Thanks for submitting this PR, it is appreciated, and sorry for not responding sooner. Looks like no one on the team has a strong opinion regarding this change. Your change does not break unit tests, so that is good, but you will need to add additional unit tests if you want to proceed. Please refer to the FAQ.

[meiskalt7]

Thanks for your answer. I will add tests for this changes ASAP.

[meiskalt7]

I added test for this pull request
link: stleary/JSON-Java-unit-test#93

[stleary]

Approved. Starting 3 day comment window.