Simplify code
Start improving hints
Add an exercise type showing equation not graph
Add method to evaluate an expression
Spell evaluate correctly
Improve hints
Add function to generate string showing how to evaluate
Improve hints to show how to evaluate each expression
More hints
Add colours to hints
Can colour rational expression strings for hints
Don't expand evaluation hints when not necessary
Fix colouring of hint
More hint colour fixes
Colour hints for graph exercise
Merge branch 'evenodd' of https://github.com/petercollingridge/khan-exercises

Conflicts:
	exercises/even_and_odd_functions.html
	utils/rational-expressions.js