Create a top-level "third_party" directory

This directory now contains third_party software that is vendored into
the Servo source tree. The idea is that it would eventually hold
webrender and other crates from mozilla-central as well with a standard
patch management approach for each.

third_party/ply/example/BASIC/basiclog.py

@@ -0,0 +1,73 @@
+# An implementation of Dartmouth BASIC (1964)
+#
+
+import sys
+sys.path.insert(0, "../..")
+
+if sys.version_info[0] >= 3:
+    raw_input = input
+
+import logging
+logging.basicConfig(
+    level=logging.INFO,
+    filename="parselog.txt",
+    filemode="w"
+)
+log = logging.getLogger()
+
+import basiclex
+import basparse
+import basinterp
+
+# If a filename has been specified, we try to run it.
+# If a runtime error occurs, we bail out and enter
+# interactive mode below
+if len(sys.argv) == 2:
+    data = open(sys.argv[1]).read()
+    prog = basparse.parse(data, debug=log)
+    if not prog:
+        raise SystemExit
+    b = basinterp.BasicInterpreter(prog)
+    try:
+        b.run()
+        raise SystemExit
+    except RuntimeError:
+        pass
+
+else:
+    b = basinterp.BasicInterpreter({})
+
+# Interactive mode.  This incrementally adds/deletes statements
+# from the program stored in the BasicInterpreter object.  In
+# addition, special commands 'NEW','LIST',and 'RUN' are added.
+# Specifying a line number with no code deletes that line from
+# the program.
+
+while 1:
+    try:
+        line = raw_input("[BASIC] ")
+    except EOFError:
+        raise SystemExit
+    if not line:
+        continue
+    line += "\n"
+    prog = basparse.parse(line, debug=log)
+    if not prog:
+        continue
+
+    keys = list(prog)
+    if keys[0] > 0:
+        b.add_statements(prog)
+    else:
+        stat = prog[keys[0]]
+        if stat[0] == 'RUN':
+            try:
+                b.run()
+            except RuntimeError:
+                pass
+        elif stat[0] == 'LIST':
+            b.list()
+        elif stat[0] == 'BLANK':
+            b.del_line(stat[1])
+        elif stat[0] == 'NEW':
+            b.new()