Don't rely on xen-dir to determine libxenstat directory

Instead, harcode paths where libxenstat.so can be found. This may not
be the most elegant solution, but it allows for our module to work
under systems that have a broken or inexistent xen-dir helper. Debian
and Ubuntu have libxenstat under /usr/lib/xen-X.X/lib, whereas CentOS
and other RPM based distro have it /usr/lib and /usr/lib64.
Bump version to 0.3.0