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

data_structures_and_algorithms/dijkstra-shortest-path.py

@@ -1,48 +0,0 @@
-from collections import deque
-from heapq import heappush, heappop
-from fixtures import weighted_graph
-
-
-def put(t, x, xs):
-    if t == 'stack':
-        return xs.append(x)
-    if t == 'queue':
-        return xs.append(x)
-    if t == 'priority':
-        return heappush(xs, x)
-
-
-def pop(t, xs):
-    if t == 'stack':
-        return xs.pop()
-    if t == 'queue':
-        return xs.popleft()
-    if t == 'priority':
-        return heappop(xs)
-
-
-# shortest_path :: Vertex -> Vertex -> Graph -> [Vertex]
-def shortest_path(a, b, g):
-    """Returns the shortest path from vertex a to vertex b in graph g."""
-    t = 'priority'
-    xs = []
-    seen = set()
-    # Map(Weight, [Vertex])
-    m = {}
-
-    put(t, (0, [a], a), xs)
-
-    while xs:
-        w0, path, v = pop(t, xs)
-
-        seen.add(v)
-        if v == b:
-            m[w0] = path
-        for w1, x in g.get(v):
-            if x not in seen:
-                put(t, (w0 + w1, path + [x], x), xs)
-
-    return m
-
-
-print(shortest_path('a', 'f', graph_a))