Added custom arguments handling in Options

[qwonix-R]

No description provided.

[SimonCropp]

why change the docs?

[qwonix-R]

changed them by accident

[SimonCropp]

can you add tests and docs for this change

[qwonix-R]

what do you mean by tests and docs?

[SimonCropp]

add tests that ensure this change works. and add documentation that explains how to use it

[qwonix-R]

i don't understand how tests look like
in my project i use it like this

var options = new Options
{
    CustomArguments = new[]
{
    "-V", "mainfont=DejaVuSans", 
    "-V", "babel-lang=russian",  
    "-V", "inputenc=utf8",       
    "-V", "header-includes=\\usepackage{ragged2e}",
    "--pdf-engine=xelatex"
}

and after just convert using this options object