Avoid overflowing read buffer decoding Bitmaps.

Fixes #283.

We use BitmapFactory.Options#inJustDecodeBounds to
decode the width and height of images before
decoding the full image so that we can downsample
large images to avoid memory pressure. To do so,
we use mark/reset on a buffered InputStream. To
handle images with large headers, we set a large
(currently 5mb) mark limit. However, there's
always the chance that that limit is insufficient
even with a well formatted image and a bug
free decoder. Since downsampling is typically an
optimization, if such a failure occurs we still
want to decode the full image, even if we can't
obtain the dimensions. By enforcing we don't read
beyond our limit, we ensure that the header read
fails recoverably, so that the full image can
still be decoded.
Fix a javadoc import error in ViewTarget.