JSON subset parser

Write a recursive-descent parser for a tiny JSON subset and return the parsed Python value. Grammar: a value is an integer (optional leading minus, no decimals), a double-quoted string with no escapes, the literals true/false/null, or an array '[' value (',' value)* ']' (arrays may be empty). There is no whitespace anywhere in the input. Map true/false to Python booleans and null to the string "null". The input is guaranteed well-formed.