Introduce QString

Introduce QString

QString is a high-level data type that can be used to represent
C strings.

The following functions are available:

- qstring_from_str() Create a new QString
- qstring_get_str()  Get a pointer to the stored string

Note that qstring_get_str() is too low-level for a data type like
this, but it's interesting for quick read-only accesses.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>