New exercise
Improve hints
Add questions with non-factored expressions
Create function for writing expressions in a factored form
Add extra hint showing factoring
Fix hints with negative numbers and denominator of 1
Merge remote-tracking branch 'upstream/master'
Update rational expression module
Function to find coefficient of specific terms
Solving rational expressions 2 exercise
Remove old exercise
Improve simplifications hints
Merge branch 'solve-rat-exp2' of https://github.com/petercollingridge/khan-exercises

Conflicts:
	utils/rational-expressions.js