the lowest 2 bits of handle values are no longer unused, and 0 is
now a valid handle value.
the first 64 handles are now reserved, and will not be automatically
allocated by the kernel. however, they are still valid handles, and
other handles can be moved to this area using an as-yet-unwritten
function. this is to allow support for standard POSIX file descriptors,
which require the values 0, 1, and 2.
all kernel headers have been moved from include/mango to include/kernel
and include definitions that are only relevant to kernel-space.
any definitions that are relevant to both kernel- and user-space
(i.e. type definitions, syscall IDs) have been moved to
include/mango within libmango.
