We want minimal static build. And this now also breaks with our openssl
since it tries to automatically dlopen some of the engine modules.

Make the libapk and lua module optional at buildtime and off by default.
This is because enabling libapk requires that mkinitfs also copies the
libapk.so or the initramfs will not work.

To build libapk:

 make LIBAPK=yes

To build lua module (will enable LIBAPK=yes):

 make LUAAPK

To link apk to libapk (will enable LIBAPK=yes):

 make SHARED_LIBAPK=yes

All the above applies to make install target as well.

Instead of having a null pointer, use a dummy array which just
says the array is empty. This helps in multiple places of the code
which would otherwise need explicitly need to check first if the
array exists. This has been cause of multiple seg.faults in the
past as the array check is easily omitted.

This also removes (or fixes) all existing checks accordingly.

also makes it possibly to upgrade package without adding it to
top-level deps. fixes #69.

this way we never change cwd, and relative filenames are always
parsed consistently. this also helps filename construction in many
places. this patch also changes '--root' to override location of
all configuration to be in the new root. previously it depended
on the file which one was used.