10x20: Process more fully.

10x20: Process more fully.

Provide a hand-edited good/10x20.sfd, generated using fontforge from
bad/6x13.sfd, which adjusts more than just ` '.

Specifically: provide a single new hand-drawn shape for the comma and
both single quotes; increase the weight of the full stop; adjust the
colon and semicolon to match.

Justifications for the changes:

 - Our primary goal is matched quotes, so at least the single quote
   (which in post-2000 10x20 is vertical) needs changing.

 - The quote glyphs in the pre-2000 10x20 are rather poor, when used
   in a matched pair.  They are rather more slanted and rather less
   tall than seems usual for quotes.  Using these for quotes results
   in an (IMO) odd appearance for quoted strings.

 - 10x20 is very like 6x13 in overall style but pre-2000 6x13 quotes
   have a rather different (and IMO better) look.

 - The comma should have the same shape as the quotes, like in 6x13.
   But in pre-2000 10x20, the comma and the single quotes have
   different shapes.

 - The pre-2000 comma is very similar to the full stop.  This makes
   them hard to distinguish at high DPI.

 - The colon and semicolon should contain exactly a full stop and a
   comma; but the pre-2000 colon and semicolon's lower marks are
   raised compared to the corresponding standalone mark.  Again, this
   is not much like 6x13.

 - The weight of the pre-2000 10x20 full stop and colon are anomalous:
   in general the weight of 10x20 is similar to that of 6x13 scaled up
   (eg, the 10x20 A has 54 pixels out of 200, 27%, compared to the
   6x13 A which has 20 pixels out of 78, 26%).  The 6x13 stop is 5
   pixels (6.4%) but the pre-2000 10x20 stop is 6 pixels (3.0%).  We
   compromise by increasing it to 9 pixels (4.5%).

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>