Log Message:
mu: updated to version 1.12.6

Packaging changes:
- removed patch due to upstream fixing bug

Upstream changes:
- improved documentation: man-pages, mu4e reference manual, README
- new function `mu4e-save-message`, to save a copy of the message at
  point
- reduce logging a bit
- fix `mu4e-compose-pre-hook` which broke with the 1.12.5 changes
- fix bookmark support (`bookmark-make-record-function`)
- fixed running mu server on non-systemd operating systems