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/sales.bas

@@ -0,0 +1,20 @@
+10 FOR I = 1 TO 3
+20 READ P(I)
+30 NEXT I
+40 FOR I = 1 TO 3
+50 FOR J = 1 TO 5
+60 READ S(I,J)
+70 NEXT J
+80 NEXT I
+90 FOR J = 1 TO 5
+100 LET S = 0
+110 FOR I = 1 TO 3
+120 LET S = S + P(I) * S(I,J)
+130 NEXT I
+140 PRINT "TOTAL SALES FOR SALESMAN"J, "$"S
+150 NEXT J
+200 DATA 1.25, 4.30, 2.50
+210 DATA 40, 20, 37, 29, 42
+220 DATA 10, 16, 3, 21, 8
+230 DATA 35, 47, 29, 16, 33
+300 END