Add hook decorator (#28)

* Add m.add_hook test

* Add @m.hook test

* Add `hook` decorator for convenience

* Update readme and examples

* Update run_callback

* Improve `add_hook` docstring

expound on callback structure

* Rm debug print

* Improve docstring

test/test_manticore.py

@@ -0,0 +1,21 @@
+import unittest
+
+from manticore import Manticore
+
+class ManticoreTest(unittest.TestCase):
+    def setUp(self):
+        self.m = Manticore('test/binaries/arguments_linux_amd64')
+
+    def test_add_hook(self):
+        def tmp(state):
+            pass
+        entry = 0x00400e40
+        self.m.add_hook(entry, tmp)
+        self.assertTrue(tmp in self.m._hooks[entry])
+
+    def test_hook_dec(self):
+        entry = 0x00400e40
+        @self.m.hook(entry)
+        def tmp(state):
+            pass
+        self.assertTrue(tmp in self.m._hooks[entry])