v0.19.3: Beta release #7

Release 0.19.1 mistakenly included in-development features (mainly, service arguments) that were not intended to be included in a bug-fix release. Release 0.19.2 did not include those features. Since distributions may be relying on the features, this release adds them back. There are a small number of documentation fixes and improvements also.

Note that service arguments support is limited, for example, they are not supported by dinitcheck at this stage. If not using those features, the recommendation is to remain on 0.19.2 for now. This release contains no bugfixes compared to 0.19.2.

Thanks to current sponsors: Paweł Zmarzły (pzmarzly), Wesley Moore (wezm), M. Herdiansyah (konimex), Coleman McFarland (dontlaugh), q66, saolof, and private sponsors.