config: add box-drawings-uses-font-glyphs=no|yes option

When disabled, we render box drawing characters ourselves. This is the
default.

When enabled, we instead use font glyphs. I.e. no special treatment.

Closes #430

doc/foot.ini.5.scd

@@ -96,6 +96,24 @@ in this order:
 	
 	Default: _0_.
 
+*box-drawings-uses-font-glyphs*
+	Boolean. When disabled, foot generates box/line drawing characters
+	itself. The are several advantages to doing this instead of using
+	font glyphs:
+	
+		- No antaliasing effects where e.g. line endpoints appear dimmer.
+		- Line- and box characters are guaranteed to span the entire cell,
+		  resulting in a gap-less appearance.
+		- No alignment issues, i.e. lines are centered when they should be.
+		- Many fonts lack some, or all, of the line- and box drawing
+		  characters, causing fallback fonts to be used, which results
+		  in out-of-place (for example, badly sized) looking glyphs.
+	
+	When enabled, box/line drawing characters are rendered using font
+	glyphs. This may result in a more uniform look, in some use cases.
+	
+	Default: _no_.
+
 *dpi-aware*
 	*auto*, *yes*, or *no*. When set to *yes*, fonts are sized using
 	the monitor's DPI, making a font of a given size have the same