Add ability to store any type as claim in JSONToken

[coveralls]

Pull Request Test Coverage Report for Build 269

• 45 of 62 (72.58%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-2.7%) to 84.956%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
json_token.go	44	61	72.13%
<!--	Total:	45	62	72.58%	-->

Files with Coverage Reduction	New Missed Lines	%
json_token.go	3	81.48%
<!--	Total:	3		-->

Totals
Change from base Build 255:	-2.7%
Covered Lines:	480
Relevant Lines:	565

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💛 - Coveralls

[BRMatt]

Thanks you for maintaining this library! Just wanted to note that this PR broke API compatibility for clients of JSONToken{}.Get(), as it now requires 2 arguments rather than just 1.

I'm not sure it helps much now that the PR has been merged into master, but I think the go mod convention for changing the public API is to cut a new major version?

[o1egl]

I know. I gonna release v2 after some refactoring. If you want to use it now, please stick to git commit instead of tags