Add "relaxed" json support

[madeso]

All of these should be optional so we can support both relaxed and strict json.

Root JSON type

• A document with types other than object and array. Root elements should be able to be any value #12

Comment

• Single line c-style comment Single line c-style comments #13
• Multiple line c-style comment Multiline c-style comments #14
• Comment handler event?
• Comment stored in Value?

Object

• Key without quotes (limited to a sequence of confined character sets, e.g. (A-Za-z-)+[0-9A-Za-z-]* String without quotes in object #17
• Extra comma at the end Extra comma at end in object #15

Array

• Extra comma at the end Extra comma at end in array #16

String

• Single quote pair Single quoted string #18
• String without quotes?

Number

• Fractions begins with ., e.g. .123 Number fractions begins with . #19
• Number with '.' but without fraction digits, e.g. 0., 123. Numbers ending with . but without fraction digits #20
• Hexadecimal integer, e.g. 0xDEADBEEF Hexadecimal integers #21
• Infinity and NaN?

Based on Tencent/rapidjson#36

[madeso]

Closing as there are already issues for all important points.

• Storing comments aren't useful so ignoring that.
• String without quotes already has a issue
• Infinity/nan sounds less useful and it is probably bad practice for writing it in a config file