Improve consistency when explicitArray + mergeAttrs are both true

When the explicitArray and mergeAttrs options are both set, ensure
that nodes introduced by attributes are put into arrays.
Use assert.strictEqual instead of assert.equal for tests

The coercions performed by assert.equal (which uses ==) make it
difficult to see whether the output is really as intended, since,
e.g., the effect of explicitArray is not visible.
Bi-directional support

(Experimental for now)

Squashed commit of the following:

commit 486a7aa628fdd0079345e8662e273b528fd6568c
Author: Jack Senechal <jack@jacksenechal.com>
Date:   Thu Oct 31 15:36:12 2013 -0700

    revert mods to test/fixtures/sample.xml

commit 3819482436cd3ccfd3a6d5410288164de578cc5e
Author: Jack Senechal <jack@jacksenechal.com>
Date:   Thu Oct 31 15:31:57 2013 -0700

    adding diff to devDependencies

commit 969a354cf15840f011bde83140b806bfa76103c9
Author: Jack Senechal <jack@jacksenechal.com>
Date:   Thu Oct 31 15:25:47 2013 -0700

    Updated README.md

commit 3f9f626e5b23a56418af9048c332ac9eebf0d0f8
Author: Jack Senechal <jack@jacksenechal.com>
Date:   Thu Oct 31 15:16:34 2013 -0700

    exposing renderOpts and fixing a few tests

commit f61b65281251ea62758586ac4149d849cc7fe0e4
Author: Jack Senechal <jack@jacksenechal.com>
Date:   Thu Oct 31 03:09:53 2013 -0700

    lots of unit tests for the builder

commit c499afd83eb28cbcd5e644dc517cc78fc78f5a85
Merge: 26626d0 a2a4938
Author: Jack Senechal <jack@jacksenechal.com>
Date:   Mon Oct 28 17:34:12 2013 -0700

    Merge remote-tracking branch 'upstream/master'
    'npm test' passing

    Conflicts:
    	README.md
    	lib/xml2js.js
    	package.json
    	src/xml2js.coffee

commit 26626d0e75b7218aa535b987321ace9e616b8ac9
Author: Jack Senechal <jack@jacksenechal.com>
Date:   Fri Oct 25 04:10:08 2013 -0700

    Cleaned up and fixed a few bugs

commit 690b1c88accbfb6d872bce4d0bc934b5dd578887
Author: setumiami <guido@bitstorm.it>
Date:   Thu Jan 10 01:39:55 2013 +0100

    README.md modified.

commit 9bc9e9fc5d1179f9ebb977500989e82d817f5e77
Author: setumiami <guido@bitstorm.it>
Date:   Thu Jan 10 01:37:10 2013 +0100

    Added bi-directional conversion (xml2js and viceversa)
Added Guido and Jack to list of contributors
Improved consistenzy with explicitArray + mergeAttrs

Many thanks to @hoelzl for spotting and fixing this.

Merge branch 'hoelzl-master'

Conflicts:
	lib/xml2js.js
Resolves #109: builder now supports partial file generation via the `fragment` option