Added command-line parameters to override the default x-width and y-width settings

[sylvainhalle]

Some documents don't have the default proportions of 1872x1404 pixels (for example, US Letter documents). Exporting the lines file as SVGs will result in lines placed at incorrect locations when superimposed onto the original PDF in those cases. The problem is solved when overriding these default settings with the proper pixel values for the document size (1805x1404 in the case of US Letter). The proposed modification allows users to specify these values as (optional) command line arguments. The default behavior of the program is left unchanged.

[sylvainhalle]

Also added possibility for more than 99 pages in output filenames