Allow set tag to use bracket notation for object properties

[hegemonic]

In the current version of Swig, if you're using the set tag to assign a value to an object's property, you can't use bracket notation for the object property. For example, if you've already set the local variables foo = {} and bar = 'bar', any of the following will cause Swig to complain about an unexpected assignment:

{% set foo[bar] = "baz" %}
{% set foo['bar'] = "baz" %}
{% set foo["bar"] = "baz" %}

This pull request makes all of those examples work as you'd expect. It still behaves correctly if a quoted property name includes an assignment operator.

If you have any feedback on this pull request, I'd be happy to amend it.

(P.S. Thanks for creating such an excellent template engine!)

[hegemonic]

I have no idea why the Travis CI build is failing on Node.js 0.8. I don't think it's related to my commit, since the tests also fail on master.

When I run the tests locally with Node.js 0.8.26, they all pass.

[bodokaiser]

@hegemonic
Have the same problem. Guess it is a small error in the tests. See: #381 (comment)

I think paul will fix this after doing his current pr work.

[paularmstrong]

Merged!

I also added the ability to mix bracket and dot-notation.

As for the Node v0.8.x issues, I may just drop official support for 0.8.x. 0.10.x has been out for some time now.

[hegemonic]

Excellent! Many thanks.