feat(string): init Rabin-Karp rolling hash

Implemented Rabin-Karp rolling hash class abstraction.

After testing muliple algorithms for efficient substring searching in a stream
abstracted by a ring buffer, I've dropped the idea of using KMP in favor of
implementing my own algorithm based of the Rabin-Karp rolling hash algorithm.

tests/unit/byteb4rb1e_utils/string/test_rolling_hash.py

@@ -0,0 +1,61 @@
+import unittest
+
+from byteb4rb1e_utils.string import RollingHash
+
+class test_compute_initial_hash(unittest.TestCase):
+    """RollingHash.compute_initial_hash()
+
+    i calculated the hashes by hand, as a basis for this test case. Hopefully
+    there's no logical flaw...
+    """
+
+    def test_default(self):
+        """computation of hash"""
+        result = RollingHash.compute_initial_hash(
+            b'abcdefg',
+            base = 31,
+            mod = 10**9 + 7
+        )
+
+        self.assertEqual(result, 988021244)
+
+class test___init__(unittest.TestCase):
+    """RollingHash.__init__()
+
+    Make sure the class instance is initialized correctly
+
+    I calculated the hashes by hand, as a basis for this test case. Hopefully
+    there's no logical flaw...
+    """
+
+    def test_default(self):
+        """computation of initial hash and highest base factor"""
+        instance = RollingHash(b'abcdefg')
+
+        self.assertEqual(instance._hash, 988021244)
+        self.assertEqual(instance._hbase_factor, 887503681)
+
+    def test_defaults_override(self):
+        """override of defaults"""
+        instance = RollingHash(
+            b'abcdefg',
+            base = 9,
+            mod = 4
+        )
+
+        self.assertEqual(instance._mod, 4)
+        self.assertEqual(instance._base, 9)
+
+
+class test_roll(unittest.TestCase):
+    """RollingHash.roll()"""
+    def test_rolling_hash(self):
+        base=31
+        mod=10**9 + 7
+
+        rh = RollingHash(b"foobar", base=base, mod=mod)
+        rolled_hash = rh.roll(ord("f"), ord("n"))
+
+        control_hash = RollingHash.compute_initial_hash(b"oobarn", base, mod)
+
+        self.assertEqual(rolled_hash, control_hash)