First leibniz part text.
Formatting; better kind projecting; preview of 2nd part.
Use long lambda syntax, disambiguated sum function name.
Show type error, pretty symbols.
Scaladoc link.
Avoid infix type application in a couple places, for clarity.
Move leibniz part 1 to today.
Merge pull request #25 from S11001001/leibniz-1

New post: "A function from type equality to Leibniz"