Add dfu bootloader update application and use absolute delay for stlink

Hello,

appended 3 patches
- adds a dfu-bootloader appliaction
- uses absolute delays when waiting for pull-up delays on the STLINK
(hopefully fixes issue #30)

Updating the dfu-bootloader by additional application is helpfull for the
STLINK, as for flashing the bootloader by SWDb otherwise jumpers need to be
soldered or external SWD is not possible.
Use like:
- dfu-util -s 0x08002000:leave -D dfu_upgrade.bin
- dfu-util -s 0x08000000:leave -D blackmagic_dfu.bin
- Push reset buttom and reconnect to enter new dfu bootloader
- dfu-util -s 0x08002000:leave -D blackmagic.bin
--
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
>From fae5022c304a8866f056ea66660ac7ce3809dcf8 Mon Sep 17 00:00:00 2001
From: Uwe Bonnes <bon@elektron.ikp.physik.tu-darmstadt.de>
Date: Sun, 20 Oct 2013 15:00:36 +0200
Subject: F1: Prepare to update dfu bootloader via DFU with additional
 application.