accdb: add some debugging to 'set'
accdb: parse assignment args
accdb: port 'set' to changesets
accdb: actually implement apply_changeset()
accdb: don't clobber `op`
accdb: drop old code and permanently switch to changesets
accdb: changeset: switch to a changelog

Previously each operator had a separate list, much like LDAP's
add/remove/replace, but this could get confusing as it ignores the
ordering of add vs remove operations in the command line.

(The previous code treated "-key" and "key=val" as sort-of barriers,
discarding all changes that would have happened previously, but it
couldn't handle "key-=val key+=val" vs "key+=val key-=val" without
becoming too complex. (Although I *do* have an idea about how it could
be implemented...))

Switch to an ordered list of changes instead. The old code might be
useful in case I ever need to work with LDAP, though.
accdb: changeset: also s/set/add/ if previous op was += or -=
accdb: changeset: add key:=value, completely useless

...but if I'm implementing this, no harm in adding another obscure
operator; it makes things more consistent anyway as all three operations
now have their own operators, and '=' is a DWIM shortcut.
Merge branch 'accdb/edit-syntax'

Switch from the crufty and hacky update syntax (seriously, parsing the
same operators twice in different ways?) into the more consistent
array assignment syntax:

    -key        (delete key)
    key+=value  (add value)
    key-=value  (remove value)
    key:=value  (set value, discarding old ones)
    key=value   (DWIM set or add value)