docs: Document coding style conventions

This patch documents some Mesa coding style conventions that came up
during the discussion of commit 67b5a32 (Perform implicit type
conversions on function call out parameters).

docs/devinfo.html

@@ -71,6 +71,13 @@ well documented.  Also, strive to write clean, easily understandable code.
 If you use tabs, set them to 8 columns
 </p>
 
+<p>
+Line width: the preferred width to fill comments and code in Mesa is 78
+columns.  Exceptions are sometimes made for clarity (e.g. tabular data is
+sometimes filled to a much larger width so that extraneous carriage returns
+don't obscure the table).
+</p>
+
 <p>
 Brace example:
 </p>
@@ -81,10 +88,26 @@ Brace example:
 	else {
 	   bar;
 	}
+
+	switch (condition) {
+	case 0:
+	   foo();
+	   break;
+
+	case 1: {
+	   ...
+	   break;
+	}
+
+	default:
+	   ...
+	   break;
+	}
 </pre>
 
 <p>
 Here's the GNU indent command which will best approximate my preferred style:
+(Note that it won't format switch statements in the preferred way)
 </p>
 <pre>
 	indent -br -i3 -npcs --no-tabs infile.c -o outfile.c