Fix possible ValueError, which wasn't caught, by extracting digits from dimensions attributes values in convert_int. Also be more liberal allowing values with px or percentage suffixes. Added test for image dimensions.
#10 apart from numbers accept values ending with px in ceonvert_to_int
just 1 call to strip
Merge pull request #10 from yaph/convertint

Fix possible ValueError in convert_to_int caused by values like 1px