Moved the sort package to under graph, because it is really a part of the graphing package semantically.
Added .settings directory which for some reason was not present.
Changed toFormat to informalToFormal for clarity.
Started the skeleton for a rework of ParsedMathFunction using the
expressions package. Here's the plan:

* On construction, a bunch of fancy-ass string parsers will convert an
  informal expression to a formal exression to a Term.
* When calculate() is called, it will use the term. There will be a lot of
  objects involved, but NO strings. Remember that this is called once for
  every pixel on the screen, so speed is a little important.
Added a working first version of the expressions package, which includes support for calculation, derivatives, and toString() representations among Terms.