rename debug() to Debug() to stop clashing with the debug submodule from Lua

reader.lua

@@ -16,6 +16,8 @@
     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 ]]--
+local v = require("luajit/lib/v")
+v.on()
 
 require "alt_getopt"
 require "pdfreader"