Fixes: #1505, #1484, #1479, #1474.
Changes:
- Full support of PDF page rectangles like
/ArtBox
etc. - New global variable TESSDATA_PREFIX for comfortably checking presence of OCR support
- Changed
Document.xref_set_key()
such that dictionary keys will physically be removed if set to value "null". - Changed
Document.extract_font()
to optionally return a dictionary (instead of a tuple).