This is required for when helpers include json-encoded variables as arguments.
As an example, imagine a template with content:

{{# str }} somekey, someidentifier, { "fullname": "{{ fullname }}" } {{/ str }}

If the fullname variable were to include the double-quote character (e.g.
John "Trevor" Doe) because of the way in which mustache renders content, it
would become:

{{# str }} somekey, someidentifier, { "fullname": "John "Trevor" Doe" } {{/ str }}

This results in an invalid JSON structure.

To work around this issue, the quote characters in the passed variable
must be escaped:

{{# str }} somekey, someidentifier, { "fullname": "John \"Trevor\" Doe" } {{/ str }}

Unfortunately, Mustache provides no way of doing so natively.

With this function, we can quote the text as appropriate:

{{# str }} somekey, someidentifier, { "fullname": {{# quote }}{{ fullname }}{{/ quote }} } {{/ str }}

This also handles the case where the quoted cont...