The 'insert' command will be better served if parse_tag_command_line
modifies a pre-populated list (of new.tags) instead of clobbering the
list outright. The sole existing caller, notmuch_tag_command, is
unaffected by this change.
Command line parsing is factored out into a function
parse_tag_command_line in tag-util.c.
There is some duplicated code eliminated in tag_query, and a bunch of
translation from using the bare tag_op structs to using that tag-utils
API.
The memory usage discipline of tag_op_list_t is never to free the
internal array of tag operations before freeing the whole list, so it
makes sense to take advantage of hierarchical de-allocation by talloc.
By not relying on the context passed into tag_parse_line, we can allow
tag_op_list_t structures to live longer than that context.
These are meant to be shared between notmuch-tag and notmuch-restore.
The bulk of the routines implement a "tag operation list" abstract
data type act as a structured representation of a set of tag
operations (typically coming from a single tag command or line of
input).
