MathML eq

I noticed that:
```
  <apply>
    <eq />
    <ci>S</ci>
    <cn>1210</cn>
  </apply>
```
doesn't seem to evaluate to: `S=1210`, but results in `undefined`,

my best guess is that equality (and inequality) expressions are not (yet) supported by mathnet.symbolics?

are there intentions to support logical expressions like <=, <, >=, !=? 

