Splice ./universe directory into ./

Manually merging:
- README.md: I added the description from universe/README.md into the heading of
  dotfiles/README.md.
- .envrc: dotfiles/.envrc was a superset of universe/.envrc
- .gitignore: Adding some of the ignored patterns from universe/.gitignore to
  dotfiles/.gitignore

Everything else here should be a simple rename.

data_structures_and_algorithms/coins.py

@@ -0,0 +1,57 @@
+import unittest
+from math import floor
+
+################################################################################
+# Solution
+################################################################################
+
+# change_possibilities :: Int -> [Int] -> Int
+def change_possibilities(n, xs):
+    combinations = [0] * (n + 1)
+    combinations[0] = 1
+
+    for x in xs:
+        for i in range(len(combinations)):
+            if i >= x:
+                combinations[i] += combinations[i - x]
+
+    return combinations[n]
+
+
+################################################################################
+# Tests
+################################################################################
+class Test(unittest.TestCase):
+
+    def test_sample_input(self):
+        actual = change_possibilities(4, (1, 2, 3))
+        expected = 4
+        self.assertEqual(actual, expected)
+
+    def test_one_way_to_make_zero_cents(self):
+        actual = change_possibilities(0, (1, 2))
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_no_ways_if_no_coins(self):
+        actual = change_possibilities(1, ())
+        expected = 0
+        self.assertEqual(actual, expected)
+
+    def test_big_coin_value(self):
+        actual = change_possibilities(5, (25, 50))
+        expected = 0
+        self.assertEqual(actual, expected)
+
+    def test_big_target_amount(self):
+        actual = change_possibilities(50, (5, 10))
+        expected = 6
+        self.assertEqual(actual, expected)
+
+    def test_change_for_one_dollar(self):
+        actual = change_possibilities(100, (1, 5, 10, 25, 50))
+        expected = 292
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)