New Image Transformation Matrix Available

Meta information for images embedded in document pages has been enriched by the so-called transformation matrix. It can be used to find out, what "happened" to the image rectangle to make it fit in its bbox on the page, like scaling and rotation.

Other changes are mostly minor bug fixes:
#990
#972

A new Page method get_image_info() is also available, which extracts image meta information from the page's TextPage - much like the corresponding Page.get_text("dict"), but without extracting any text or the image binary data themselves.