fixes tests and adds support for multi-line content

This pull request updates the tests to use JSON.stringify() instead of JSON.toString(). Using toString() returns the JSON library as a string, '[object JSON]', not the JSON string of the parameter, so the tests where never failing.

This pull request also adds support for multi-line content as mentioned in the [spec](http://tools.ietf.org/html/rfc5545); ([3.1](http://tools.ietf.org/html/rfc5545#section-3.1)) defines the ability to have a single content line that is "folded" over multiple lines.

Tests have been added and the library has been updated to support multi-line content.