Add support for int colors in themes

Allow theme colors to be specified as integers.

Works with both decimal & hex. Given the XXX warning, it seems
reasonable to allow users to specify their theme’s colors as the base
integers since the names are pretty arbitrary.

We changed the variable name `ul` to `col_value` per @H3rnand3zzz
suggestion.

src/config/color.c

@@ -361,8 +361,19 @@ find_closest_col(int h, int s, int l)
 static int
 find_col(const char* col_name, int n)
 {
+    char* endptr;
+    unsigned long col_value = strtoul(col_name, &endptr, 0);
     char name[32] = { 0 };
 
+    /*
+     * When the col_name is a uint8, then we don’t need to look up by
+     * color name (which is problematic given the duplicate names)
+     */
+
+    if ((*endptr == '\0' || *endptr == '\n') && col_value <= UINT8_MAX) {
+        return (int)col_value;
+    }
+
     /*
      * make a null terminated version of col_name. we don't want to
      * use strNcasecmp because we could end up matching blue3 with