Buffer rework and start network
Add Icmp
Net: Dhcp working
Start Tcp
Overhaul timer
Get Tcp Echo Server Working
Net stack refactoring

Just move things into separate files and comment a little
Replace network port allocator
Clean port allocation
Fix bug in IP header calculation
Fix early tcp pcb removal bug
Separate out network apps
Pull apart tcp server app receivers
Add Makefiles for net apps
Make UniqueIOBuf allocate once

Use MakeUniqueIOBuf to create a UniqueIOBuf which allocates the
descriptor and data contiguously to save on an extra memory allocation.
Fix bug in cleanup
Restructure NetTCP
Remove dead code
Add TCP client and complete active open/close
Fix timeout calculation bug