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.

universe/data_structures_and_algorithms/delete-node.py

@@ -1,60 +0,0 @@
-import unittest
-
-
-################################################################################
-# Solution
-################################################################################
-def delete_node(x):
-    if not x.next:
-        raise Exception('Cannot delete the last node in a linked list.')
-    else:
-        x.value = x.next.value
-        x.next = x.next.next
-
-
-################################################################################
-# Tests
-################################################################################
-class Test(unittest.TestCase):
-    class LinkedListNode(object):
-        def __init__(self, value, next=None):
-            self.value = value
-            self.next = next
-
-        def get_values(self):
-            node = self
-            values = []
-            while node is not None:
-                values.append(node.value)
-                node = node.next
-            return values
-
-    def setUp(self):
-        self.fourth = Test.LinkedListNode(4)
-        self.third = Test.LinkedListNode(3, self.fourth)
-        self.second = Test.LinkedListNode(2, self.third)
-        self.first = Test.LinkedListNode(1, self.second)
-
-    def test_node_at_beginning(self):
-        delete_node(self.first)
-        actual = self.first.get_values()
-        expected = [2, 3, 4]
-        self.assertEqual(actual, expected)
-
-    def test_node_in_middle(self):
-        delete_node(self.second)
-        actual = self.first.get_values()
-        expected = [1, 3, 4]
-        self.assertEqual(actual, expected)
-
-    def test_node_at_end(self):
-        with self.assertRaises(Exception):
-            delete_node(self.fourth)
-
-    def test_one_node_in_list(self):
-        unique = Test.LinkedListNode(1)
-        with self.assertRaises(Exception):
-            delete_node(unique)
-
-
-unittest.main(verbosity=2)