Escaping, table layout, and document fixes

Quoted Klammertext specials (^@ ^| ^# ^^ ^: ^*) and ^'...'^ regions now
survive re-processing (held as escape markers until final output);
:after_apply phase functions receive and return raw target text.

Tables: :hpos element position (center|left|right|<length>) replaces the
unimplemented :center/:indent; the ranged cell override is renamed
:justify; :column_width works in html (colgroup widths) and gains
'fill' -- the remaining width, capped at the column's widest entry, in
both targets; a table wider than the text column warns on the console;
table edges without an outer line set their text flush on the margins.

@document: no empty title bar for untitled documents; @vfill fills to
the bottom of the window in html (pure CSS); @vspace in plain text;
new @dot klammer; monospace email links.

sks/kutil/kutil.k

@@ -35,6 +35,16 @@
   #:python_cast (lambda s : [__import__("kutil").parse_length("tex", e) for e in s.split()])
 @@@
 
+@@@argtype element_hpos |
+  the horizontal position of a block element (a table or an image) within
+  the text column: center, left, right, or a length, which places the
+  element's left edge that far from the left margin (e.g. ^:hpos 4em, ^:hpos
+  .25w).  When the element is as wide as the text column, the positions are
+  indistinguishable.
+  :pattern center^|left^|right^|'length'
+  :default center
+@@@
+
 @@@argtype figure_id |
 an identifier for a figure.