Returns a Boyer-Moore-Horspool matcher which searches the (special)
simple-string STRING for the first occurence of the substring
PATTERN. The search starts at the position START-POS within STRING
and stops before END-POS is reached. Depending on the second
argument the search is case-insensitive or not. If the special
variable USE-BMH-MATCHERS is NIL, use the standard SEARCH function
instead. (BMH matchers are faster but need much more space.)