Adding xmllint properties + minor stuff

Details.

*** wsdler_generetors:

A schema always need root element. Added generator function to handle
this case.

The string restriction generetor was missing the xsd quilification.

Fixed string generation where min and max length are equal.

Temporarily changed char generation to only emit ascii. This was do
to debugging purposes, where my Erlang unicode foo is not strong
enough.

*** wsdler_xsdfile_tests:

Added property based testing of some simple type strings, where the
property is that xmllint can validate the generated output. This is
good :-).