feat: add support for DjVu image format #94
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This PR adds support for the DjVu image format.
According to DjVuLibre (an open-source implementation of DjVu), "DjVu is a web-centric format and software platform for distributing documents and images. DjVu can advantageously replace PDF, PS, TIFF, JPEG, and GIF for distributing scanned documents, digital documents, or high-resolution pictures. DjVu content downloads faster, displays and renders faster, looks nicer on a screen, and consume less client resources than competing formats. DjVu images display instantly and can be smoothly zoomed and panned with no lengthy re-rendering. DjVu is used by hundreds of academic, commercial, governmental, and non-commercial web sites around the world."
According to Wikipedia, the signature for DjVu files is
41 54 26 54 46 4F 52 4D ?? ?? ?? ?? 44 4A 56.NOTE: Similar to TIFF files, DjVu images can either be single-paged or multi-paged, where the byte following the signature above is either
55(U) for single-page or4D(M) for multi-page images; this PR includes tests for both.