Update parallel processing api (#246)

* Remove m.workers, add run(procs=), update docs

* Update docs

examples/script/count_instructions.py

@@ -17,13 +17,12 @@ if __name__ == '__main__':
         sys.exit(2)
 
     m = Manticore(sys.argv[1])
-    m.workers = 3
     m.context['count'] = 0
 
     @m.hook(None)
     def explore(state):
         m.context['count'] += 1
 
-    m.run()
+    m.run(procs=3)
 
     print "Executed ", m.context['count'], " instructions."

examples/script/google2016_unbreakable/win.py

@@ -58,5 +58,4 @@ def hook(state):
     # We found the flag, no need to continue execution
     m.terminate()
 
-m.workers = 10
-m.run()
+m.run(procs=10)