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/html_util.py

@@ -193,8 +193,27 @@ def element_tag(element):
 def font_class(font):
     return {"r" : "", "i" : "ritalic", "t" : "monospace", "s" : "sanserif"}[font]
 
+def hpos_container(element, hpos):
+    # Wrap element in its horizontal-position container.  hpos is left,
+    # center, right, none, or a length, which becomes the left margin
+    # (the tex counterparts are the \LTleft glue for tables and the
+    # \hspace* in latex_util.caption_wrapper).
+    style = None
+    if hpos not in ("left", "center", "right", "none"):
+        length, _, _ = kutil.parse_length("html", hpos, 1)
+        style = f"margin-left: {length}"
+        hpos = "indent"
+    result = E("div").cls("hpos_" + hpos).body(element)
+    if style:
+        result.attr("style", style)
+    if hpos not in ("center", "indent"):
+        result.cls("hpos_margin")
+    return result
+
+
 def add_caption(element, caption_label, number, caption_text,
-                font_symbol="i", hpos="center", side="bottom", as_string=True, font_size=.9):
+                font_symbol="i", hpos="center", side="bottom", as_string=True,
+                font_size=.9, width=None, max_width=None):
     tag = element_tag(element)
     # Caption
     caption = ""
@@ -232,12 +251,19 @@ def add_caption(element, caption_label, number, caption_text,
         #print("-"*80)
 
         element = E("div").cls("caption_" + side).attr("data-label", caption_label).body(element)
+        if width:
+            # The element's width (e.g. a table's :column_width total) lives
+            # on this wrapper: the element fills it, and the caption tracks
+            # the element.
+            element.attr("style", f"width: {width}")
+        elif max_width:
+            # A content-sized element (a 'fill' table): the wrapper shrinks
+            # to it but never past the text column, so the element wraps at
+            # narrow windows instead of overflowing.
+            element.attr("style", f"max-width: {max_width}")
 
 
-    result = element
-    result = E("div").cls("hpos_" + hpos).body(element)
-    if hpos != "center":
-        result = result.cls("hpos_margin")
+    result = hpos_container(element, hpos)
 
     if number:
         result.cls("element_container")