improved history

this is the control center: the variables above define how the diffs behaves. 
@splitters defines the pieces of the text that we compare. It's words, html tags, inclusions and links. 
The @disjunction_pattern identifies the pieces that we don't compare but that we want to keep in the diff (white spaces). @exclude_pattern does the same but it breaks the <del> and <add> tags. For example if we want to keep html tags but don't want to compare them then when ever an html tag appears we close <del>s and <add>s and reopen them after the html tag.