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/target/latex_util.py

@@ -55,15 +55,21 @@ def minipage(content, width="\\textwidth", vertical="c", center=True, vmargin=""
     return result
 
 def caption_wrapper(element, hpos, bottom_margin=.67):
+    # hpos is left, center, right, none (no wrapper), or a length, which
+    # becomes the left margin.  The element is a box on a line inside a
+    # full-width minipage; \hfill on the empty side pushes it into place.
     vmargin = f"{bottom_margin}\\baselineskip"
-    result = element
     if hpos == "center":
-        result = minipage(element, vmargin=vmargin)
-    elif hpos == "left":
-        result = minipage("\\hfill" + element, vmargin=vmargin)
-    elif hpos == "right":
-        result = minipage(element + "\\hfill", vmargin=vmargin)
-    return result
+        return minipage(element, vmargin=vmargin)
+    if hpos == "left":
+        return minipage(element + "\\hfill", vmargin=vmargin, center=False)
+    if hpos == "right":
+        return minipage("\\hfill" + element, vmargin=vmargin, center=False)
+    if hpos == "none":
+        return element
+    length, _, _ = kutil.parse_length("tex", hpos, 1)
+    return minipage(f"\\hspace*{{{length}}}" + element + "\\hfill",
+                    vmargin=vmargin, center=False)
 
 def make_caption_text(number, label, text, font_symbol, font_size):
     caption = None