Improve parsing error message

[iwahbe]

This PR significantly improves the readability of parsing error messages.

The old message looked like this:

‘jsonian--path’: Unexpected character ’u’

The new error message looks like this:

jsonian-find: unexpected character ’e’ at 5:14: expecting literal value "true"
  "fizz": [twue, 2, "3", false, { "some": "object" }],
              ^