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/fixtures.py

@@ -1,110 +0,0 @@
-# Using this module to store commonly used, but annoying to create, data
-# structures for my test inputs.
-#
-# Use like:
-# from fixtures import graph_a
-
-################################################################################
-# Constants
-################################################################################
-
-edge_list = [
-    ('a', 'b'),
-    ('a', 'c'),
-    ('a', 'e'),
-    ('b', 'c'),
-    ('b', 'd'),
-    ('c', 'e'),
-    ('d', 'f'),
-    ('e', 'd'),
-    ('e', 'f'),
-]
-
-unweighted_graph = {
-    'a': {'b', 'c', 'e'},
-    'b': {'c', 'd'},
-    'c': {'e'},
-    'd': {'f'},
-    'e': {'d', 'f'},
-    'f': set(),
-}
-
-adjacencies = {
-    'a': {
-        'a': False,
-        'b': False
-    },
-    'a': [],
-    'a': [],
-    'a': [],
-    'a': [],
-    'a': [],
-    'a': [],
-}
-
-weighted_graph = {
-    'a': {(4, 'b'), (2, 'c'), (4, 'e')},
-    'b': {(5, 'c'), (10, 'd')},
-    'c': {(3, 'e')},
-    'd': {(11, 'f')},
-    'e': {(4, 'd'), (5, 'f')},
-    'f': set(),
-}
-
-# This is `weighted_graph` with each of its weighted edges "expanded".
-expanded_weights_graph = {
-    'a': ['b-1', 'c-1', 'e-1'],
-    'b-1': ['b-2'],
-    'b-2': ['b-3'],
-    'b-3': ['b'],
-    'c-1': ['c'],
-    'e-1': ['e-2'],
-    'e-2': ['e-3'],
-    'e-3': ['e'],
-    # and so on...
-}
-
-unweighted_digraph = {
-    '5': {'2', '0'},
-    '4': {'0', '1'},
-    '3': {'1'},
-    '2': {'3'},
-    '1': set(),
-    '0': set(),
-}
-
-################################################################################
-# Functions
-################################################################################
-
-
-def vertices(xs):
-    result = set()
-    for a, b in xs:
-        result.add(a)
-        result.add(b)
-    return result
-
-
-def edges_to_neighbors(xs):
-    result = {v: set() for v in vertices(xs)}
-    for a, b in xs:
-        result[a].add(b)
-    return result
-
-
-def neighbors_to_edges(xs):
-    result = []
-    for k, ys in xs.items():
-        for y in ys:
-            result.append((k, y))
-    return result
-
-
-def edges_to_adjacencies(xs):
-    return xs
-
-
-# Skipping handling adjacencies because I cannot think of a reasonable use-case
-# for it when the vertex labels are items other than integers. I can think of
-# ways of handling this, but none excite me.