Moved body scoring

Moved it to the score function from the main function because it feels
more appropriate to organize it this way.
Created find-best-element.js

Moved code out of calamine.js, modularized the code, moved out a nested
function, improved the clarity of the code, updated dependencies, added
some clarifying comments
Created unwrap-elements.js

Moved the code out of the transformDocument so that it delegates to
unwrapElements.
Added calamine/unwrap-elements.js

Forgot to do this earlier when creating the new file
Minor improvements

Moing out invariants, less nested functions, better names, comments