Write hpet timer twice

This allows booting with implementations that require them to be set separately.
Also, check for the availability of legacy-replacement mode and periodic interrupts before using hpet

Fix issues with SIGCONT

Add clippy lints, action some clippy items

Check if current namespace exists

Move null and zero from kernel space to user space

Page table optimization

Add documentation on using gdb

Do not discard .debug section

Do not discard the .debug section. If the builder would like to discard
this section, they can do so explicitly with objcopy.

Update debugging code

Fix for the latest nightly

elf.rs: do not inline constant from goblin library

SELFMAG is declared [here](https://github.com/m4b/goblin/blob/de8aecc8f1e7f3de7d66a1511d3976cdf0335e0c/src/elf/header.rs#L91).