Fixed:

* align: fix logging and `--dump-json` #82
* align: avoid superfluous TextEquiv #76
* binarize: traverse regions in reading-order (so derived images are, too)
* ocrolib.morph.spread_labels: fix when no labels exist
* ocrolib.morph.label: :fire: fix ncomps (+1)
* ocrolib.morph.select_regions: fix `dtype` for just 1 label
* binarize/denoise/deskew/dewarp/segment: skip zero-size segments to avoid numpy problems
* common.compute_hlines/separators: fix h/v kernel size
* common.compute_hlines/separators: early length filter must be softer than final criterion
* segment: fix reference before assignment when partitioning
* segment: set correct pageId for image files
* segment (region level): fix and speed up horizontal merging
* segment (page/table level): continue more gracefully when recursive XY-cut fails
* segment (page/table level): fix significance criterion for partitions' line labels
* segment (page level): prevent empty `ReadingOrder` group
* segment (page level): avoid adding existing regions to RO group unless they are immediate children
* resegment: skip empty line polygons
* resegment: prevent overflow in numpy slices due to rounding errors when cropping #79
* resegment: set correct pageId for image files #80
* resegment: use `set_points` to ensure invalidating existing line images
* polygon_for_parent: ensure path validity before checking consistency
* polygon_for_parent: ensure valid polygons for new coords
* segment/polygon_for_parent: skip segment if polygon cannot be made valid

Changed:

* clip: avoid suppressing overlapping components on both sides
* clip: require independence instead of `min_fraction` threshold
* deskew: delegate to OCR-D/core for reflection and rotation
* dewarp: expose `smoothness` parameter
* segment (region level): ignore separators and other existing regions
* segment: do not suppress neighbours if they cover the segment completely
* segment: do not suppress neighbours if already clipped
* segment (region level): annotate clipped images on region level, too
* segment (region level): improve horizontal merging (transitivity, don't cross separators, enlarge region mask, too)
* segment (page/table level): avoid grouping new text lines with existing regions in a XY-cut
* segment (page/table level): re-order grouped new and existing regions in a XY-cut
* segment (page/table level): avoid creating convex hulls for new regions if these would create additional overlaps with existing regions
* segment (page level): hmerge line labels (within each region) here, too
* segment: upgrade segmentation failures from warning to error
* ocrolib.morph: add `dist_labels` (distance transform of semantic segmentation
* ocrolib.morph: for CC analysis, use 4-way instead of 8-way connectivity
* ocrolib.morph: new function `rb_reconstruction` based on repeated dilation and masking
* common.compute_images/hlines/separators: use that instead of `spread_labels`
* re/segment: before spreading lines, assign diacritics to seeds below
* resegment: :tada: complete rewrite (now polygonal and global):
  - polygonal calculus instead of pixel/morphology operations (for efficiency)
  - optimise assignments globally instead of locally (to avoid conflicting assignments)
  - add param `level-of-operation` with new level `page`, also as new default
  - suppress all non-text regions and non-text non-regions before text line segmentation
  - on page level, merge horizontally adjacent labels, but avoid creating new region conflicts in doing so
  - general algorithm: 
    * after line segmentation, find contours and polygonalize, then compare overlaps once
    * allow assigning multiple new labels to existing lines and combine them via a (slightly concave) hull polygon
    * assign existing lines to new lines such that among those candidates covering high fg (90%) and bg (60%) shares of  the new line, the one with the largest fg and bg share of the existing line wins
    * bail out of resegmentation if the new polygon would loose a share of `threshold` fg or `threshold / 3` bg, or if some new, but unassigned line would be lost entirely 
    * subtract matching lines from non-matching lines
* resegment: allow detection of colseps if some regions exist already
* resegment: :tada: compute true alpha shape instead of eroded convex hull
* resegment: :tada: implement alternative `method=ccomps`:
  - calculate connected component analysis
  - calculate distance transform of existing labels
  - find new line seeds by flattening existing labels (via maximum distance)
  - propagate line seeds across connected components (by majority in case of conflict)
  - spread ccomps labels against each other into background
  - for each line,
    * if enough background and foreground wille be retained
    * find the hull polygon of the new line via alpha shape
    * annotate as new coordinates
* resegment: :tada: implement alternative `method=baseline`:
  - calculate connected component analysis
  - find new line seeds based on the existing baselines (by applying dilation above)
  - propagate line seeds across connected components (by majority in case of conflict)
  - spread ccomps labels against each other into the background
  - for each line,
    * if enough background and foreground will be retained
    * find the hull polygon of the new line via alpha shape
    * annotate as new coordinates
* segment (page/table level): :tada: improve splitting by separators:
  - when trying to partition slices by separators,
     * also treat pre-existing regions like separators, and
     * fix the condition on smallest allowed partitions (insignificant but complete lines)
  - fall back to (new) topological partitioning
    * when no cut or separator-split partition can be found for the current slice, then attempt to find another separator-split by grouping lines along their mutual horizontal neighbourship with fg separators
  - repeatedly allow both kinds of partitioning, if interspersed