better handling of malformed pdf

• fix for not correctly encapsulated graphics
• fix for non standard referenced media boxes

Remove some warnings

see #15

Support pdf-reader 2.0

0.1.0

update pdf-reader to 2.0

Working for prawn 2.2.1

• more code needed to be rescued as it had been removed from mainline
• work around frozen array VALID_OPTIONS

Working against 2.1.0

no new features where added

no issues where specifically fixed