Use (and fix) the LED support.

In the bootloader, the led is turned on when entering the main loop and turned
off when leaving. This coste 6 bytes for devices with a LED.

Upgrade will also turn on the LED when entering, but then toggles it for every
page written to flash. It also turns off the LED when leaving.

Added the LED defines for my '167 and '861 configurations.
mnflash: step further to building a libmnflash.

* prefix all public symbols with "mnflash"

* renamed some functions/types too

* move library source to "lib/"

* move includes to "include/libmnflash"
  ... would also work if the includes were in "/usr/include/libmnflash"

* adjust Makefile accordingly

* low-noise stuff in Makefile
libmnflash: allow custom filters in mnflash_usb_connect()

... also add an example how to use it.

This change allows one to write a custom function to identify a device, which
then can be brought into the bootloader and be upgraded.

The stuff in "example/" illustrates how that can be done.
Remove objects that should not have been added and add .gitignore.
libmnflash: shared library, pkg-config support, install

* build a shared library when ENABLE_SHARED is defined.

* added an "install" target to the Makefile
  ... also supports DESTDIR for easier distribution packaging. Knows
  about "prefix" and other autoconf-style variables.

* install package-config support file "mnflash.pc"
  ... and use that in the example.