Support JSON5

[jasperhabicht]

• Allow hexadecimal numbers
• Allow leading + and . as well as trailing . in numbers
• Allow strings delimited with single quotation marks (where inside a string delimited by single quotes a double quote needs not to be escaped and vice versa)
• Allow Infinity and NaN
• Allow JS IdentifierName as key
• Allow \x-style Unicode sequences
• Allow U+2028, U+2029, U+FEFF and Zs category as whitespace
• Allow comments

[jasperhabicht]

With version 1.6.6, sockets have been implemented that allow preparsing. This may be a way to define a plug for JSON5.