Implement json5 spec

[adhocore]

Already supported

• single/multi line comments
• trailing commas in array/object
• literal new lines in multiline string

New features (implemented in #2)

• unquoted object key
• single quoted key
• single quoted value
• signed positive number
• trailing decimal point number
• leading decimal point number
• hexadecimal number

To be implemented

• infinity
• NaN
• unicode escape
• other whitespace