better output for 'unable to parse json'

[jehiah]

When data is unable to be parsed, the bytes are output which isn't helpful when you want some human readable output of what the record was.

[simonschmidt]

How about outputting the bytes as a string together with the line number?

$ ./json2csv -k 'a,b' <<< '{ "a":: 1, "b": 2}'
2014/01/08 11:18:14 ERROR Decoding JSON at line 1: invalid character ':' looking for beginning of value
{ "a":: 1, "b": 2}