simple string tokenizer

 String::Tokenizer is a simple string tokenizer which takes a string and splits
 it on whitespace. It also optionally takes a string of characters to use as
 delimiters, and returns them with the token set as well. This allows for
 splitting the string in many different ways.
 .
 This is a very basic tokenizer, so more complex needs should be either
 addressed with a custom written tokenizer or post-processing of the output
 generated by this module. Basically, this will not fill everyones needs, but
 it spans a gap between simple split / /, $string and the other options that
 involve much larger and complex modules.
 .
 Also note that this is not a lexical analyser. Many people confuse
 tokenization with lexical analysis. A tokenizer mearly splits its input into
 specific chunks, a lexical analyzer classifies those chunks. Sometimes these
 two steps are combined, but not here.