Overview of changes in 1.50.4, 09-02-2022
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* Tweak synthetic space sizes
* itemize: Try harder to avoid NULL fonts
* docs: Some additions
* Pass synthetic slant to harfbuzz
* Make sloped carets work with uneven scales
* Fix serialiation on arm
* Avoid an uninitialized variable warning
* Reinstate previous behavior of pango_attr_list_splice
* Deprecated pango_coverage_ref/unref
* Fix serialization on non-glibc systems
* Fix allow-breaks handling