Log Message:
mail/aerc: Update to 0.17.0

Improve HOMEPAGE and do some cleanups while here.

Prepared in wip by Kevin Bloom.

Added:
- New flagged criteria for :sort
- New :send-keys command to control embedded terminals
- Account aliases now support fnmatch-style wild cards
- New :suspend command bound to C-z by default
- Disable parent context bindings by declaring them empty
- Toggle folding with :fold -t
- mail-deleted hook that triggers when a message is removed/moved from a
  folder
- mail-added hook that triggers when a message is added to a folder
- Customize key to trigger completion with $complete in binds.conf
- Setting `complete-min-chars=manual` in aerc.conf now disables automatic
  completion, leaving only manually triggered completion
- .ThreadUnread is now available in templates
- Allow binding commands to Alt+<number> keys
- AERC_ACCOUNT and AERC_ADDRESS_BOOK_CMD are now defined in the editor's
  environment when composing a message
- Reply with a different account than the current one with `:reply -A
  <account>`
- New [ui].tab-title-viewer setting to configure the message viewer
  tab title
- The {{.Subject}} template is evaluated to the new option
  [ui].empty-subject if the subject is empty
- Change to a folder of another account with `:cf -a <account> <folder>`
- Patch management with :patch
- Add file path to messages using {{.Filename}}
- :menu command to invoke other ex-commands based on a shell command
  output
- CLI flags to override paths to config files.
- Automatically attach signing key with pgp-attach-key in accounts.conf
- Copy messages across accounts with `:cp -a <account> <folder>`
- Move messages across accounts with `:mv -a <account> <folder>`
- Support the "draft" flag
- Thread arrow prefixes are now fully configurable

Fixed:
- Selection of headers in composer after :compose -e followed by :edit -E.
- Don't lose child messages of non-queried parents in notmuch threads
- Notmuch folders defined by the query `*`

Changed:
- :open and :pipe commands are now executed with `sh -c`.
- Viewer tab title shows (no subject) if there is no subject
- Signature placement is now controlled via {{.Signature}}