MathQuill parser parses sin x^2 incorrectly

[nathancarter]

The MathQuill parser does not correctly prioritize exponentiation over trig function application.

Input: sin x sup 2

Output:

<OMA>
  <OMS cd="arith1" name="power"/>
  <OMA>
    <OMS cd="transc1" name="sin"/>
    <OMV name="x"/>
  </OMA>
  <OMI>2</OMI>
</OMA>

Expected output:

<OMA>
  <OMS cd="transc1" name="sin"/>
  <OMA>
    <OMS cd="arith1" name="power"/>
    <OMV name="x"/>
    <OMI>2</OMI>
  </OMA>
</OMA>

Steps we should take:

1. Add a unit test to demonstrate this failure.
2. Fix the definition in the source code.
3. Ensure the new unit test now passes.
4. Commit and push.