Summary of changes:
- kernel/mem renamed to kernel/mm
- consolidated page/frame defs into one file which now lives in the
kernel/mm package and is referenced by both pmm and vmm pkgs
- consolidated parts of the vmm code (e.g. PDT+PTE)
- memcopy/memset helpers moved to the kernel package
- physical allocators moved to the kernel/mm/pmm package
- break vmm -> pmm pkg dependency by moving AllocFrame() into the mm
package.
Things like error messages (e.g in the io pkg) are actually allocated
when init() is executed. Unless we trigger a call to init(), values like
this will be nil causing various problems when we try to use functions
from the stdlib.
By setting up pwd as a Go workspace, we can trim import paths from
something like "github.com/achilleasa/gopher-os/kernel" to just
"kernel".
These changes make forking easier and also allows us to move the code to
a different git hosting provider without having to rewrite the imports.
