Changed exception message for EOF in string literal

Signed-off-by: Stuart Sierra <mail@stuartsierra.com>
added tests for EOF in unterminated strings and arrays

Signed-off-by: Stuart Sierra <mail@stuartsierra.com>
Remove tests for specific error messages

Even though that was the point of the previous commit, I don't want to
declare that any specific error message string is part of the public
API. Only the type of the exception is specified.