commands: one grammar for !, merged commands, a settings sheet, two-level help

A `!` now means force or everything and nothing else (`:w!`, `:search!`,
`:export!`, `:logout!`). A command that did a second thing behind its bang
takes a word for it instead: `:space new|name|rm`, `:list name|rm`,
`:task [add]|edit`, `:upload seal`, `:import zip [/]`. `:card` while reading
a document makes a card about it, so `:card!` is gone.

Merged: `:export` downloads what has focus, a file as it is or a document as
markdown (`:download` folded in); `:share [off|new]` replaces `:unshare` and
`:link`, and the list's `s` and `y` give way to it and the info sheet;
`:noh` replaces `:clear`; `:vault [unlock|lock|passwd]` replaces `:unlock`,
`:lock` and `:passwd`; Esc in the list puts down what `m` picked up before it
closes the document, replacing `:unmark`.

The old spellings run as their new lines for one release through a table in
commands.ts; help and Tab leave them out, and the wiki lists them.

A settings sheet (`,` or `:settings`) holds the options, the vault, the
backup, the signed-in browsers, ssh keys and capture tokens. Each row runs
the command a line would. Bare `:set`, `:vault`, `:backup`, `:sessions`,
`:sshkey` and `:token` open it at their part.

`?` shows the keys and commands to start with, flagged in the keymap and the
command table; a second `?` (or `:help all`) shows all of them, and a filter
always searches all of them. Help rows are keyed by key and description, as
two contexts can share a label.

docs/wiki/Spaces-and-Documents.md

@@ -10,8 +10,8 @@ uni do not get mixed up.
   `Shift-Tab` step through them.
 - `w` shows every space at once, with what was last written in each. `hjkl`
   move, `Enter` goes there.
-- `:space! <name>` makes a space, `:name! <name>` renames the one you are in,
-  and `:rmspace` puts it in the trash with everything in it. Two spaces cannot
+- `:space new <name>` makes a space, `:space name <name>` renames the one you are in,
+  and `:space rm` puts it in the trash with everything in it. Two spaces cannot
   share a name, whatever the case.
 - `:set noboard` turns the board off for a space, `:set board` back on.