add make genpath rules, .path files, updated .top and .year

Add .path files to each winner directory: a file containing
the path to the winner directory from the top directory.

Changed YYYY/.year files to contain the paths, from the top
directory, if the winning directories for the given year.

Changed `/.top` to contain the IOCCC years.

Added `make genpath` rule to the top Makefile and the
year Makefiles to generate the above.

Added FAQ 6.8 to `faq.md` to explain the above.

Updated manifest to reflect recent changes to the list of files.

2000/.year

@@ -1 +1,14 @@
-2000
+2000/anderson
+2000/bellard
+2000/bmeyer
+2000/briddlebane
+2000/dhyang
+2000/dlowe
+2000/jarijyrki
+2000/natori
+2000/primenum
+2000/rince
+2000/robison
+2000/schneiderwent
+2000/thadgavin
+2000/tomx