* libc/time/time.tex: Improve the documentation.
* libc/time/strftime.c: Improve the documentation.
(iso_year_adjust): New helper function.
(strftime): Simplify '%E' and '%O'. Change '%c' to use
recursion. Fix '%C', '%y', and '%Y' to deal with years with more
than 4 characters. Combine '%d' and '%e'. Implement '%D', '%F',
'%g', '%G', '%n', '%R', '%t', '%T', '%u', '%V', '%X', and '%z'.
Avoid core dumps on valid inputs (maxsize == 0, or
tim_p->tm_isdst > 1).
f1d439fc64