Fixed bug with matching the end of a string

Getting the diff between these strings...

"abc def"
"abc def ghi"

would result in it copying "abc" and then replacing "def" with "def ghi"
when it should copy "abd def" and then insert " ghi".

This was because whitespace (i.e. the delimiters) were being included on the end of the fragments, rather than being treated as fragments in their own right. So "def" != "def " hence no match. By allowing the delimiters to form fragments, and the correct differences are recognised. Delimiter fragments are now seen as "soft-matches" (i.e. they can match as part of a longer matching span only) to avoid long runs of non-matching text being treated as non-matching words separated by matching whitespce (which would make for absurdly complex diffs).