Separate name/value options

Since parsing the command as an array, the :name_value options:
(:cover and :post)
were being parsed to something like:

["/bin/wkhtmltopdf", "-q", "--cookie", "_session_id 383934", ...]
Which wouldn't work.

Split these options so it is called like this:
["/bin/wkhtmltopdf", "-q", "--cookie", "_session_id", "383934", ...]