string parser does not recognize uncompliant strings #12

The Readme currently states:

Furthermore, we allow for more escape symbols in strings as the JSON specification. While this may not be a problem in reality, we are aware of it, but as long as we have a hand-written parser, we won't invest too much to be fully compliant.

And in fact, anything between two unescaped quotes will be treated as strings. However, the JSON standard is very explicit how a string may look like:

As long as the class does not implement this string specification, the class is not fully JSON compliant.