Allow null to be the value of an embedded item.
Allow a link element to be an array of links. See 'admin' link element in the spec: http://stateless.co/hal_specification.html#examples
Reworked _addData() method to correct a couple problems and simplify:

When data consists of nested, associative arrays, the keys that were outputted into XML were incorrect. When a top level element contained an array containing string elements, _addData() failed because it was expected the values of the array to be arrays themselves.
Merge pull request #8 from johnshopkins/fix-resource-issues

Fix resource issues
Version 0.3.2
Removed version property from composer.json

This will enable versions for composer/packagist to be managed soley by
tags and no longer require the version property to be updated manaually.
This subsequently resolves future issues with tagged releases from not
showing up due to forgoted version updates to the `composer.json`
PSR2 edits and docblock updates

 - Updated docblocks to reflect the current API and signatures.
 - Updated minor edits for PSR2 compliance.
 - Added IETF Draft proposal link to readme.
Merge pull request #10 from zircote/feature/remove-composer.json-version-property

Removed version property from composer.json
More CS fixes for PSR-2
Merge pull request #11 from zircote/feature/api-doc-blocks-cleanup

PSR2 edits and docblock updates
Adding the JSON_NUMERIC_CHECK flag in __toJson so that numberic strings are properly converted to numbers.
Expands on #7 for numeric conversions of JSON

This PR is linked to #7 providing the ability to actively enable
`JSON_NUMERIC_CONVERSION` while passively it is disabled.

Resolves #7
Merge remote-tracking branch 'origin/feature/json_numeric_check-default-off' into feature/json_numeric_check-default-off