Exercise string handling functions

foo          = ABCDEF
strlen(foo)  = 6
substr(foo,3,4) = CD

haystack     = `date`
haystack     = Fri Oct 23 23:56:01 UTC 2015
needle       = :
S = strstrt(haystack,needle) = 14
haystack[S-2:S+2] = 23:56
It is now 23:56

words(haystack)   = 6
word(haystack,5)  = UTC

sprintf output of long strings works OK

