Handle `CallExpression` for debug macros.

[rwjblue]

Currently, we are handling only ExpressionStatement's for debug macro replacement. Unfortunately, the following do not get processed (since they do not include an ExpressionStatement):

function foo() {
  return assert(false, 'derp'); // ReturnStatement
}

let qux = () => assert(false, 'herp'); // ArrowFunctionExpression

This is the underlying issue in emberjs/ember-cli-babel#168.

[josex2r]

Hi, I think I found a way to fix the issue in branch BBVAEngineering/use-call-expression, but I'm not sure if it's the correct way.
I was unable to use CallExpression at first level, don't know why but babel wasn't removing some line breaks :S

Then I tried another approach, use the visitors ReturnStatement and ArrowFunctionExpression to find the CallExpression and replace the debug functions.

All the tests seems to work but I couldn't try the branch in ember apps because when I link my package (npm link) to an Ember app the proccess always breaks with an exception:

Build Error (Babel) in ember-resolver/features.js # Any Ember package
Cannot read property '__esModule' of undefined

¿Any hints about linking this package to a project to test my branch?

[josex2r]

Finally I could check the changes, 3f902db was driving me crazy XD
It seems to be working fine in different apps so I've opened #56.