Streamline eval functions

[blink1073]

Major streamline of the eval logic on both the python and matlab ends. Consolidates to a single path.

Only API change: there is no more content.code output parameter for run_code calls.

[blink1073]

Question: does eval need to exist at all since it can be called using feval similar to get_variable? The only downside I see is we'd lose the content.code parameter in the return value.

[blink1073]

The symmetry was too good to pass up.

[blink1073]

I don't know what is going on with Coveralls all of a sudden.

[isbadawi]

Coveralls is just complaining the coverage % went down (just barely), but whatever.

LGTM.

[blink1073]

I've seen coverage drop before and it did not call it a failure, maybe they changed their policy (I hope not).