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.