Use binary mode for temporary files when using pdf_from_string

Use binary mode for temporary files when using pdf_from_string
Updated readme for proper pdf_from_string usage

LGTM given by: @armyofgnomes, @nhance

Squashed commit of the following:

commit 0259857426714f3f5aa04e83da4c3a0460adc094
Author: Valentino <valentino@reenhanced.com>
Date:   Thu Jun 27 14:03:10 2013 -0400

    Fix spacing in readme changes

commit 030029db20be324f137a101d23513e428b3e5e0f
Author: Valentino <valentino@reenhanced.com>
Date:   Thu Jun 27 13:52:27 2013 -0400

    Updated README with correct way to use pdf_from_string

commit 9030e65b08ad9f94df515852c4993932d7793dca
Author: Valentino <valentino@reenhanced.com>
Date:   Thu Jun 27 10:34:49 2013 -0400

    Use binary mode for temporary files when using pdf_from_string