More mail flags can now be set, unset, and toggled, not just the
read/seen flag.
This functionality is implemented with a new `:flag` and `:unflag`
command, which are extensions to the matching `:read` and `:unread`
commands, adding support for different flags. In fact, the
`read`/`unread` commands are now recognized aliases to `flag`/`unflag`.
The new commands are also well documented in aerc(1).
The change mostly extends the previous read/unread setting functionality
by adding a selection for the flag to change.
For some reason the current code frequently segfaults due to an
invalid C memory address. This commit mediates that by never keeping an object
alive longer than absolutely necessary.
Notmuch only allows a single write connection, all other clients trying to
modify the db block. Hence we should only open one when we actually need it.
Apparently we also need to refresh the RO DB connection upon modification,
else we get stale message tag results
This commit introduces the notmuch backend.
The backend is conditionally compiled in if the "notmuch" tag is provided.
Most of the message types are implemented, with the notable exceptions
of DeleteMessages as well as any copy / move / append type.
Reason being, that those aren't normally applicable in a notmuch based workflow.
Changes v2 --> v3, based on review comments
* Use account config for configuration
