Fix various kernel warnings.

See merge request !125

Use #[repr(packed)] with correct alignment for paging.

See merge request !124

Fix conditional compilation without the acpi feature.

See merge request !122

bump raw-cpuid dep to avoid pulling in serde

See merge request !121

Multi core

See merge request !118

Support the I/O APIC alongside the 8259 PIC

See merge request !117

since this would require pcid to know the _PRT (PCI routing table) to
use and map the interrupt pins to the correct IRQs. xhcid is unaffected
by this though, since it uses MSI-X.

All ACPI handling will be done in userspace before the infrastructure
necessary would make sense (I don't think adding serde to the kernel
would be optimal, and how else would all of the ACPI namespace be
parsed?).

and fix a typo that prevented multiple tables from being listed
correctly.