improve memtest target

Make sure the makefile does not encounter any false errors, and make
the valgrind calls run --quiet, so we do not get as much redundant
output.
add -w --no-warnings option

This option makes sure that no warnings are printed to the console,
which can be useful when testing for- or compiling edge cases, where
a warning would only clutter the output.
print warning when using pin i/o w/o power config

If the CHECK or SET command is used without having specified a vin
and ground we issue a warning. This is because many chips will not
function as expected if they do have any power connected.

Since this warning will also clutter the output of a lot of test
cases we also add the -w flag to all the program calls to avoid
unnecessary warnings in the output.
change variables in the makefile

Remove the explicit declaration of the C-compiler $(CC), since make
will take care of that for us and we (hopefully) do not use anything
specific to gcc.

Furthermore change the name of CC_FLAGS and LC_FLAGS to their standard
make names.
make test targets depend on the program

Since the program needs to be there in order to run the tests, we
might as well make it a dependency for running them.
write the README