Refactor of Quoted Literal String Handling and More tests

This PR fixes the internal representation of a Quoted String Literal from a strangely quoted string to an instance of `\Handlebars\String`.

This should move the some of the complexity I previously added to the `\Handlbars\Context::get` method into `\Handlebars\Template::parseArguments`

`Template::parseAruments` on 

    {{#ifEquals var "Some Value"}}

Previously would have resulted in 

    ["var", '"Some Value"']

And `Context::get` treated it as a string literal based on the string staring and ending with a quote. 

Now parseArguments results in 

    ["var", new \Handlebars\String("Some Value")]

and Context::get treats instances of Handlebars\String as string literals. 

Also added a couple of new test cases to test the previously uncovered `Template::parseArguments`  and added to existing test cases.