This release mainly affects seriesmeta and the new covergen tool.
Seriesmeta now works even before books are imported (i.e. you don't have to reconnect to update series metadata for new books), and it now supports EPUB3-style series metadata. macOS is now supported as well
Covergen (re)generates cover images for nickel, with optional stretching to fit a specific aspect ratio (I use 1.5). It works on both EPUBs and KEPUBs. This speeds up browsing the library, and if stretching is used, will also make it more consistent. In addition, covergen is useful when the automatically generated cover images are not satisfactory (too small, white margins, etc).
In addition, the README has been completely redone.