v2.6

Breaking changes:

• bashy-core:
  • arg-processor:
    • New recommended processing call process-args "$@" || exit "$?", because
      of "magic" reduction noted below.
    • Renamed --init to --default, which is a better word for the meaning.
    • Removed opt-choice, as it's now covered by the more general opt-alias
      (see below).
  • define-usage: Dropped "magical" exit behavior.

Other notable changes:

• Cleaned up existing doc and added a handful more.
• bashy-core:
  • arg-processor:
    • Tightened up error checking and reporting.
    • Added opt-alias to allow for expansion of single no-value options into
      multiple options (including with values). Used underlying facility to
      rework implementation of single-character short options.
    • Added opt-multi to accept multi-valued options. Relatedly, added
      multi-value option passing syntax --opt-name[]=..., along with helper
      function vals for use sites.
  • define-usage: New option --with-help to help reduce boilerplate.
  • stderr-msg: New option --file-line.
  • Added a lot of tests, covering almost all of the core library functionality.