Feature request: better error position

[kokizzu]

The current error shows:

&json5.SyntaxError{msg:"invalid character 't' after object key:value pair", Offset:1208}
panic: invalid character 't' after object key:value pair

It would be nice if, instead of offset, there are line, column and past 10 and next 10 characters also, for example:

&json5.SyntaxError{msg:"invalid character 't' after object key:value pair", 
Offset:1208, Line: 40, Column: 1, detail: `
title:""
tooltip:"E-
^
`}
panic: invalid character 't' after object key:value pair