[ilya-fiveisky]

Motivated by the fact that examples/JSONTest.agda didn't type-check, JSON related stuff was modified in a way similar to other formats in examples, i.e.:

1. Text.Parser.JSON now uses Parser from Text.Parser instead of one from Text.Parser.Types.
2. JSONTest.agda from examples was renamed to JSONIO.agda (because, honestly, it's more IO usage example than JSON parser usage) with corresponding fixes in the code.
3. Added JSON.agda to examples with runParser usage example. I didn't use ∈ here (as in other examples) because runParser usage is what potential user would like to see in examples instead of diving into ∈ definition in order to see how it really parses a string.