I have text with paragraphs physically represented as single long
lines. I'd like to get a readable diff between each version of the
text similar to this:

paragraph 1, starting from char 203:
-... to make certain that ...
+... to make it certain that ...

In other words, if there is only small change between the two version
of a paragraph (e.g. add/delete/change one or two words), don't show
all the content of the two paragraphs.

Can I do this with a combination of simple Unix commands (or with some
sed or perl magic)? Note: I don't want to represent my paragraphs in
72- or 80-column-wrapped lines.