Fixes rewrite for es6 code

[akiellor]

It looks like this issue stemmed from us using different AST parsers for different features:

• Rewrite is using falafel, whose default is Acorn
• Esprima is used everywhere else

This PR migrates away from Acorn for rewrite by providing an esprima parser.

This PR creates an internal interface for parsing/walking which centralises control of which parser implementation we use and how we walk the AST.

[akiellor]

@jimfleming Any thoughts on this one?

[brettlangdon]

@akiellor do these updates cause any changes to the style guide?

[akiellor]

@brettlangdon I reran the grunt fmt task and no changes were present...so I don't think so.

[brettlangdon]

Cool. I'll see if I can take a deeper look a little later today, but from a glance this looks good.

[akiellor]

FYI: This is to make the esprima tree compatible with falafel's update fn's. Not sure if this sort of thing should be upstreamed to falafel.

[brettlangdon]

This is probably alright to leave here, but if you could add a comment stating that fact.

[akiellor]

done

[brettlangdon]

I ran locally and had some changes to the style guide. Can you please run grunt fmt again?

This is the diff I got from it:

diff --git a/examples/styleGuide.js b/examples/styleGuide.js
index 5a10605..b6cb6f6 100644
--- a/examples/styleGuide.js
+++ b/examples/styleGuide.js
@@ -88,8 +88,7 @@
     myVar.toString() +
     '</li>');

-  var myVar = new myVarTypes[
-    'A type']();
+  var myVar = new myVarTypes['A type']();

   callFunc(
     'An arg',

Which I am content with this change.

[brettlangdon]

Great, I think the only other request I have is. Do you mind squashing your commits down to a single commit? There are 10 here already for this change, squashing to one will make it easier to digest next time we dig through history :)

[akiellor]

done

[brettlangdon]

Cool, will merge right now. However I do not have push rights to npm. I will open an issue for @jimfleming to bump version and push.

[akiellor]

awesome...my team has been looking forward for this for a while now :)

Thanks for the quick responses!