Development:Numerical question units and intervals

This is my proposal for how the numerical question function and interface should be improved.

[_]Allow evaluation of expressions

 Checking this would accept  5/2   0.5*5  5^2/2   5^(5-3)/2  25*10^-1  sqrt(25)/2

[_] Translate "½" as "+.5" and

Answer 1:[__2.5___] Accepted error ± [0.5] Grade: [100%] Feedback:

Answer 2: Accepted error ± Grade: Feedback:

.... Answer 10: Accepted error ± Grade: Feedback:

[_] differentiated unit feedback, which is all of:

All of:  [_] feedback for lacking unit [_]Feedback for accepted UNIT but wrong number 
         [_] feedback for "possibly right number" if unit is adjusted     

Unit: [ ] (optional)

Alternative Units: Multiplier:[ ] Unit: [ Multiplier: Unit: Multiplier: Unit: Multiplier: Unit: Multiplier: Unit: