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.

.top

@@ -1 +1,27 @@
-IOCCC
+1984
+1985
+1986
+1987
+1988
+1989
+1990
+1991
+1992
+1993
+1994
+1995
+1996
+1998
+2000
+2001
+2004
+2005
+2006
+2011
+2012
+2013
+2014
+2015
+2018
+2019
+2020