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

deepmind/part_one/inflight-entertainment.py

@@ -1,51 +0,0 @@
-import unittest
-
-
-def can_two_movies_fill_flight(xs, t):
-    seeking = set()
-    for x in xs:
-        if x in seeking:
-            return True
-        else:
-            seeking.add(t - x)
-    return False
-
-
-# Tests
-
-
-class Test(unittest.TestCase):
-    def test_short_flight(self):
-        result = can_two_movies_fill_flight([2, 4], 1)
-        self.assertFalse(result)
-
-    def test_long_flight(self):
-        result = can_two_movies_fill_flight([2, 4], 6)
-        self.assertTrue(result)
-
-    def test_one_movie_half_flight_length(self):
-        result = can_two_movies_fill_flight([3, 8], 6)
-        self.assertFalse(result)
-
-    def test_two_movies_half_flight_length(self):
-        result = can_two_movies_fill_flight([3, 8, 3], 6)
-        self.assertTrue(result)
-
-    def test_lots_of_possible_pairs(self):
-        result = can_two_movies_fill_flight([1, 2, 3, 4, 5, 6], 7)
-        self.assertTrue(result)
-
-    def test_not_using_first_movie(self):
-        result = can_two_movies_fill_flight([4, 3, 2], 5)
-        self.assertTrue(result)
-
-    def test_only_one_movie(self):
-        result = can_two_movies_fill_flight([6], 6)
-        self.assertFalse(result)
-
-    def test_no_movies(self):
-        result = can_two_movies_fill_flight([], 2)
-        self.assertFalse(result)
-
-
-unittest.main(verbosity=2)