Add support of micro VMs

A network driver is developed based on the Virtio Over MMIO interface, which is part of the Virtual I/O Device Specification. Details are published at https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html

This network driver doesn't depend on the PCI bus and can be used within micro VMs. The current version is developed and tested on Qemu's microvm virtual platform. Details are published at https://qemu.readthedocs.io/en/latest/system/i386/microvm.html

The current version can be tested with the example web server of RustyHermit's Git repository. Please use following command to build the web server:

cargo build --no-default-features --features smoltcp -p httpd
Afterwards, the following command starts the web server withinthe microvm:

qemu-system-x86_64 -M microvm,x-option-roms=off,pit=off,pic=off,rtc=on,auto-kernel-cmdline=off -global virtio-mmio.force-legacy=off -nodefaults -no-user-config -display none -smp 1 -m 1G -serial stdio -kernel loader/target/x86_64-unknown-hermit-loader/debug/rusty-loader -initrd target/x86_64-unknown-hermit/debug/httpd -enable-kvm -cpu host -device isa-debug-exit,iobase=0xf4,iosize=0x04 -netdev tap,id=tap10,ifname=tap10,script=no,downscript=no -device virtio-net-device,netdev=tap10

add support of nightly-2021-08-31

redesign of the network interface

- using async tasks to check the network device

rename kernel target

- fixed bug in the CI

improve code quality

- take ExceptionStackFrames by value
- inprove the documentation

revise the code to increase the readability

- update several crate

Use stabilized `hint::spin_loop` instead of deprecated `atomic::spin_loop_hint`

- using the latest version of the crate `x86`

switch to the latest version of the nightly compiler

release v0.3.46

- Fix broken rdrand implementation (#154)
- revise VGA interface (#153)
- add network driver for the Realteck device 8139 (#150)
- add option to disable SMP support (#142)
- using a exponential backoff to realize a spinlock (#131)

add the option to disable FSGSBASE support

performance improvements

- revision of the memory subsystem initialization to avoid false sharing
- using a exponential backoff to realize a spinlock
- improving the performace of basic functions (e.g. memcpy)

required changes to support the latest nightly compiler

add system call to determine the priority of a task

add function to block and to unblock a task

- add minor modifications to support the latest nightly compiler

revise allocator to support the latest version of libstd

add syscalls to create cryptographicly secure random numbers

- add syscalls to create cryptographicly secure random numbers #96
- add integration tests
- avoid deadlock when multiple cores are available #106

add dependency to the trait  for the implementation of spinlocks

remove dependency to the feature "nakes functions"

improve the performance of the network interface