Added missing FormatString() method.

stringbuilder.mod/stringbuilder.bmx

@@ -504,6 +504,15 @@ Public
 		Return Self
 	End Method
 
+	Rem
+	bbdoc: Appends a #String value to the string builder using the specified printf style @formatText.
+	about: @formatText is limited to 256 character bytes. Formatted text is limited to 2048 character bytes.
+	End Rem
+	Method FormatString:TStringBuilder(formatText:String, value:String)
+		bmx_stringbuilder_format_string(buffer, formatText, value)
+		Return Self
+	End Method
+
 	Rem
 	bbdoc: Appends a #Byte value to the string builder using the specified printf style @formatText.
 	about: @formatText is limited to 256 character bytes. Formatted text is limited to 2048 character bytes.