Alot

* fix bad GPG signatures for mails with attachments
* new theme-files + tags section syntax
* re-introduce "highlighting" of thread lines in search mode
* new global command "call" to directly call and bind python commands
* add new buffers to direct neighbourhood of current one
* fix sanitize --spawn for X11-less use
* add new hook 'touch_external_cmdlist'
* make statusline configurable
* fix update result count after tag operations in search mode
* add config options and hooks for reply/forward subject generation
* add config options and hook for quoting messages in replies/forwards
* allow True/False/None values for boolean command parameters
* new config option "attachment_prefix"
* various small fixes for libmagic, header encoding and decoding

* use separate database for each write-queue entry when flushing
* fix behaviour of editor spawning
* fix opening of attachments in thread buffer
* fix pre_edit_translate hook
* fix opening of attachments without filename Content-Disposition parm
* clean up and complete theming (bindings help/envelope/mainframe body)
* fix datetime decoding issues
* fix abort commands on pre-hook exceptions
* fix correct default sendmail command to 'sendmail -t'
* use '> ' instead of '>' to quote in replies/fwds
* fix path completer wrt spaces in paths
* fix UI when no buffers are open
* fix issue with buffer type changing between flushes
* support multiple addresses per abook contact when using 'abook' completer
* smarter timestamp pretty printer
* new hook 'timestamp_format'
* merge multiple cc/to headers into one when displaying
* respect NOTMUCH_CONFIG env var
* smarter parsing of edited header values
* allow for singleton lists without trailing comma in config
* fix reverse-date sorted content in threadline if displayed
* emacs-style C-a and C-E in prompts
* added ability to sign outgoing mails via PGP/MIME

* revised config syntax!
* config file validation, better feedback on malformed configs
* themes read from separate files in their own (validated) syntax
* complete mailcap compatibility
* user manual
* direct addressbook type that parses `abook`s contacts
* completion for multiple recipients via AbooksCompleter
* completion for optional command parameter
* generate and set a Message-ID header when constructing mails
* add User-Agent header by default
* add sent and saved draft mails to the notmuch index and add custom tags
* guess file encodings with libmagic
* new thread mode command: "remove" to delete messages from the index
* new thread mode command: "editnew" e.g. to continue drafts (bound to 'n')
* new thread mode command: "togglesource" to display raw messages (bound to 'h')
* virtual "Tags" header for print and pipeto commands via --add_tags parameter
* much improved pipeto command in thread mode
* --spawn parameter for reply,forward,compose,editnew in thread mode
* --no-flush parameter for delayed flushing in tag,untag,toggletags commands
* make "signature as attachment" configurable; --omit_signature parameter for compose
* new envelope command: "save" to save as draft (bound to 'P')
* --no-refocus and --spawn parameter for edit in envelope mode
* header key completion for set/unset in envelope buffer
* "Me" substitution for ones own name/address in authors string
* new search mode command and search argument: "sort"
* renamed search mode command 'toggletag' to "toggletags"
* new search mode commands: "tag" and "untag"
* custom tagstring representation: hiding, substitution, colours, multi-matching