Do not crash on ASCII85 in inline images and properly support their colorspaces

[dhdaines]

Pull request

ASCII85Decode was not properly handled in inline images (because the end tag "EI\n" is very frequently present in ASCII85 streams) causing random crashing.

Also inline images weren't properly being extracted as BMP because we weren't recognizing their abbreviated colorspaces.

Fixes #1008

How Has This Been Tested?

There's a unit test ;-)

Checklist

• [ x ] I have read CONTRIBUTING.md.
• [ X ] I have added a concise human-readable description of the change to CHANGELOG.md.
• [ x ] I have tested that this fix is effective or that this feature works.
• [ x ] I have added docstrings to newly created methods and classes.
• [ x ] I have updated the README.md and the readthedocs documentation. Or verified that this is not necessary.

[pietermarsman]

Hi,

Thanks for this contribution! It is looking good but I need some more time to understand the details of this change.

[pietermarsman]

I've updated the comments and the CHANGELOG a bit.

Thanks for fixing this!