Make an option to avoid layer separation for some pages?

Make minidjvu accept filenames with spaces, probablly sequentially rename
files immediately after conversion

Use graphicsmagick instead of imagemagick as an _option_ (not as a
replacements as in pool requests)

Set compress options separtately for bw and color

Simplify: remove OCR

"Poor Man Multithread": utility like 'img2djvupmm' which
 counts files,
 divides with excess with 't' as a result,
 adds excess to first number,
 makes t dirs,
 symlinks to the first dir maximal number of files,
 symlinks to others equal numbers of files,
 runs 'img2djvu' simultaneously on each,
 glues results
