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/trickling-water.py

@@ -0,0 +1,38 @@
+class Node(object):
+    def __init__(self, value, children=[]):
+        self.value = value
+        self.children = children
+
+
+################################################################################
+# Solution
+################################################################################
+def trip_time(node):
+    s = []
+    result = 0
+    s.append((node.value, node))
+    while s:
+        p, node = s.pop()
+        if not node.children:
+            result = max(result, p)
+        for x in node.children:
+            s.append((p + x.value, x))
+    return result
+
+
+################################################################################
+# Tests
+################################################################################
+tree = Node(
+    0,
+    children=[
+        Node(5, children=[Node(6)]),
+        Node(2, children=[
+            Node(6),
+            Node(10),
+        ]),
+        Node(3, children=[Node(2, children=[Node(11)])]),
+    ])
+
+assert trip_time(tree) == 16
+print("Tests pass!")