sort-by-letters – Bibliography styles for alphabetic sorting

This bun­dle con­tains sev­eral bib­li­og­ra­phy styles for sep­a­rat­ing a doc­u­ment’s ref­er­ences by the first let­ter of the first au­thor/ed­i­tor in the bib­li­og­ra­phy en­try. The styles are adapted from stan­dard ones or from nat­bib ones.