Tidy up structure of briefcase

I had a spare fifteen minutes and decided that I should tidy up my
monorepo. The work of tidying up is not finished; this is a small step in the
right direction.

TL;DR
- Created a tools directory
- Created a scratch directory (see README.md for more information)
- Added README.md to third_party
- Renamed delete_dotfile_symlinks -> symlinkManager
- Packaged symlinkManager as an executable symlink-mgr using buildGo

scratch/data_structures_and_algorithms/shortest-path-inject-vertices.py

@@ -0,0 +1,94 @@
+from heapq import heappush, heappop
+from collections import deque
+from fixtures import weighted_graph, expanded_weights_graph
+
+# UnweightedGraph(a) :: Map(a, Set(a))
+# WeightedGraph(a) :: Map(a, Set(a))
+
+
+# shortest_path_dijkstra :: Vertex -> Vertex -> WeightedGraph(Vertex)
+def shortest_path_dijkstra(a, b, g):
+    q = []
+    seen = set()
+
+    heappush(q, (0, a, [a]))
+
+    while q:
+        w0, v0, path = heappop(q)
+        if v0 in seen:
+            continue
+        elif v0 == b:
+            return w0, path
+        for w1, v1 in g.get(v0):
+            heappush(q, (w0 + w1, v1, path + [v1]))
+        seen.add(v0)
+    return 'weighted', 'pizza'
+
+
+# expand_edge :: Vertex -> (Weight, Vertex) -> Map(Vertex, [Vertex])
+def expand_edge(v0, wv):
+    w, v1 = wv
+    assert w > 1
+
+    result = {v0: ['{}-{}'.format(v1, 1)]}
+    for x in range(w - 2):
+        result['{}-{}'.format(v1, x + 1)] = ['{}-{}'.format(v1, x + 2)]
+    result['{}-{}'.format(v1, w - 1)] = [v1]
+
+    return result
+
+
+# expand_weights :: Vertex -> WeightedGraph(Vertex) -> UnweightedGraph(Vertex)
+def expand_weights(v, g):
+    result = {}
+    q = deque()
+    seen = set()
+
+    q.append(v)
+    while q:
+        v = d.popleft()
+        if v in seen:
+            continue
+        x = expand_edge(v, g.get)
+        for w, v1 in g.get(v):
+            if w > 1:
+                ws = expand_edge(v, (w, v1))
+                result = {**result, **ws}
+            q.append(v)
+        pass
+
+
+# shortest_path_inject :: Vertex -> Vertex -> WeightedGraph(Vertex)
+def shortest_path_inject(a, b, g):
+    q = deque()
+    seen = set()
+
+    q.append((a, [a]))
+
+    while q:
+        v0, path = q.popleft()
+        if v0 == 'dummy':
+            continue
+        elif v0 in seen:
+            continue
+        elif v0 == b:
+            return len(path), path
+        for _, v1 in g.get(v0):
+            q.append((v1, path + [v1]))
+        seen.add(v0)
+        continue
+
+    return None, None
+
+
+print(expand_edge('a', (4, 'b')))
+print(expand_edge('a', (5, 'e')))
+assert expand_weights('a', weighted_graph) == expanded_weights_graph
+# a = 'a'
+# b = 'd'
+# w, x = shortest_path_dijkstra(a, b, weighted_graph)
+# w1, x1 = shortest_path_inject(a, b, weighted_graph)
+# print("[dijkstra]  Shortest path from {} to {} is {} with weight {}".format(
+#     a, b, x, w))
+# print("[injection] Shortest path from {} to {} is {} with weight {}".format(
+#     a, b, x1, w1))