Added get_value_of_key

[iboB]

it's a pretty common function when writing code to parse the json. In the test I added it's also shown what I write very often when using this function:

objval.get_value_of_key(literal("b")).get_integer_value()

[chadaustin]

Nice!

[iboB]

Thanks! btw I have added several more features locally. Should I make a single pull request for all of them or make one for each?

[chadaustin]

Hi @iboB, sorry for the delay. In terms of pull requests, I'd probably slight prefer individual ones, but it's up to you. :)