count

  Write a static method called count that takes as
    parameters a target string and a source string and that returns a count of
    the number of occurrences of the target string in the source string.  For
    example, the following call:

        count("i", "Mississippi")

   should return 4 because there are 4 occurrences of the string "i" in the
   string "Mississippi".  Your method should ignore case when comparing
   strings.  For example, the call:

        count("iss", "MISSISSIPPI")

   should return 2 because there are two occurrences of "iss" in
   "MISSISSIPPI".  Your method should consider all possible starting positions
   for the target string.  For example, given the following call:

        count("EE", "EeEeE")

   Your method should return the value 4 because there are 4 different
   locations where the string "ee" occurs in the string "EeEeE" (starting at
   index 0, index 1, index 2, and index 3).

   You may assume that the target string is not empty.  Recall that the String
   class has the following useful methods:

        charAt(index)            character at a specific index
        endsWith(text)           whether or not the string ends with some text
        equals(text)             whether or not the string equals given text
        equalsIgnoreCase(text)   whether or not the string equals given text
                                 ignoring case
        indexOf(text)            index of a particular string (-1 if not found)
        length()                 number of characters in the string
        startsWith(text)         whether or not string starts with some text
        substring(start, stop)   characters from start index (inclusive) to
                                 stop index (exclusive)
        substring(start)         characters from start index (inclusive) to end
                                 of string
        toLowerCase()            a new string with all lowercase letters
        toUpperCase()            a new string with all uppercase letters