see #100

put some emphasis on choosing an image and support flashing any 4M image
externally.

This feels like the last piece of the puzzle in chip-detection.

Fixes #82

While I think I have initially used 128 from some libreboot docs and never
had problems with it, I don't really see anybody use less than 512 right
now.

This fixes a memory leak and the output in case the flash chip is not
found by our scripts.

It feelds a little more streamlined when not repeating everything the
user does.

We've had a double-quote issue there

Fixes #31

Now our scripts start with _where_ it should be run. x230_*.sh should
be run on the x230 where Skulls should be installed. external_*.sh
obviously not.

This also adds the -f <flasher> option and an interactive menu if not
specified.

Also, this updates our script commands in the documentation and moves the
"flashrom chip config" section under the "background" section.

Closes #26

we stick with set -e so we need to catch errors manually if need be

This adds an experimental option to choose a chip from flashrom's list
using our own heuristics. If successful this should become the default
behaviour when when "-c" is not specified.

Basically this should completely replace the documentation section
"flashrom chip config" at some point.

Adresses issue #26

flashrom might do it anyways, but we have the read image and can
make sure the user didn't by accident provide the other image, for
example.