Include Makefile.local for local configuration

Makefile

@@ -15,7 +15,12 @@
 #  You should have received a copy of the GNU General Public License
 #  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-LIBEVENT=/usr/local
+-include Makefile.local
+
+GMP ?= /usr/local
+CUDA ?= /usr/local/cuda
+LIBEVENT ?= /usr/local
+CXX ?= g++
 
 WORDS = 24