Allow min_width of a block in i3bar to be a string

With this change, min_width can either be an integer (as usual), or a
string. In the latter case, the width of the text given by min_width
determines the minimum width of the block. This way one does not have to
figure out a minimum width by trial and error, only to do it again every
time the font is changed.

docs/i3bar-protocol

@@ -140,6 +140,10 @@ min_width::
 	will be padded to the left and/or the right side, according to the +align+
 	key. This is useful when you want to prevent the whole status line to shift
 	when value take more or less space between each iteration.
+        The value can also be a string. In this case, the width of the text given
+        by +min_width+ determines the minimum width of the block. This is useful
+        when you want to set a sensible minimum width regardless of which font you
+        are using, and at what particular size.
 align::
 	Align text on the +center+ (default), +right+ or +left+ of the block, when
 	the minimum width of the latter, specified by the +min_width+ key, is not
@@ -178,6 +182,17 @@ of the i3bar protocol.
 }
 ------------------------------------------
 
+In the following example, the longest (widest) possible value of the block is
+used to set the minimum width:
+
+------------------------------------------
+{
+ "full_text": "CPU 4%",
+ "min_width": "CPU 100%",
+ "align": "left"
+}
+------------------------------------------
+
 An example of a block which uses all possible entries follows:
 
 *Example*:

i3bar/src/child.c

@@ -147,6 +147,10 @@ static int stdin_string(void *context, const unsigned char *val, unsigned int le
         } else {
             ctx->block.align = ALIGN_CENTER;
         }
+    } else if (strcasecmp(ctx->last_map_key, "min_width") == 0) {
+        i3String *text = i3string_from_utf8_with_length((const char *)val, len);
+        ctx->block.min_width = (uint32_t)predict_text_width(text);
+        i3string_free(text);
     }
     return 1;
 }