More detailed parser log

[wipe2238]

JSON parser: expected ',' or ']', found other token. : json : JSON@ parseValue(Token@[]@, uint&inout)

Would be nice to see line/column in log, or maybe some piece of file where mistake was found; tracking what and where is wrong would be bit easier.

[JovankaB]

Would be nice if it was looking for the position of the given token only if error occured, and not keeping track of column and line offset during parsing (which I think would be a bit wasteful).