Add pretty printing capability

[stokesman]

These changes add the ability to pretty print the results of json2php and a unit test for such use cases.

Here's one place interest in this feature has been expressed: WordPress/wordpress-develop#2252 (comment)

If you'd be open to merging this I'd be glad to update the docs as part of the PR.

Quick example:

const printer = json2php.make({linebreak:'\n', indent:'\t'})
printer({one: 3, two: 20, three: [9, 3, 2]})

/* result:
array(
	'one' => 3, 
	'two' => 20, 
	'set' => array(
		9, 
		3, 
		2
	)
)
*/

[daniel-zahariev]

Hi, @stokesman, this looks great!
I'll be able to review tomorrow and very likely merge.

[stokesman]

Thanks @daniel-zahariev! I just pushed 9442df4 to make it a little prettier.

[daniel-zahariev]

@stokesman, thank you for your contribution 🙏🏻
I had to do some clean up and was time constrained so went the easy route and did the changes in the code myself.
Please, forgive me for that. I've added you to the list of contributors.

[stokesman]

All good, thanks for adding the feature!